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86 Cards in this Set
- Front
- Back
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Explain the term enantiomers
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Enantiomers are isomers whose structures are mirror images of one another that are non-superimposable.
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What happens when iron (III) chloride solution is added to a phenol?
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A purple solution is formed.
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What can be used to test for a carboxylic acid?
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Add sodium carbonate solution if there is a carboxylic acid group present a salt, water and carbon dioxide gas (can be seen as fizzing) will be formed.
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How does hydrogen cyanide react with carbonyl's?
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Aldehydes and ketones undergo nucleophillic addition reactions with hydrogen cyanide in the presence of an alkali such as water. Hydrogen cyanide is a weak acid that partially dissociates to form H+ and CN- ions. The CN- ion is a nucleophile so it attacks a partially positive carbon atom and donates a pair of electrons. Two electrons from the double bond is transferred to the oxygen. Hydrogen ions from water then bond to the oxygen to form a hydroxyl group.
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How can a rate equation show that a reaction involves a multi-step mechanism?
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The rate determining step is the slow step and it only involves the species present in the rate equation as they they affect the rate. Therefore, any other species that is required in the reaction but is not present in the rate equation is involved in a faster step.
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Why does an addition reaction have 100% atom economy?
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Only one product is formed in the reaction.
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Why does a hydrolysis reaction have an atom economy less that 100%
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Condensation occurs and two products are formed.
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Why is it important for reactions to have a high atom economy?
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It reduces the amount of waste product formed and the cost effective as less energy is used.
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What happens in an electrochemical cell?
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Electrons flow from the negative terminal to the positive terminal. The more reactive metal is oxidised and the less reactive metal is reduced.
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What are the standard conditions for measuring the cell potential of an electrochemical cell.
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Temperature at 298K, Pressure at 1 atm and the concentration of all ions should be 1moldm-3.
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How do you calculate the cell potential of an electrochemical cell?
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Take the more positive value away from the more negative value.
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State the colour of copper (II) ions in water and explain why the solution has this colour.
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The colour is blue this is because copper(II) ions absorb orange light and transmit blue light as it's the complementary colour.
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Describe how colorimetry is used to determine the concentration of a solution.
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Make up standard solutions of known concentrations and one unknown concentration.
Choose a suitable filter. Zero the colorimeter with distilled water. Measure the absorbance of standard solutions. Plot calibration curve. Read the concentration of the unknown solution from the calibration curve. |
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How does a phosphate group combine with a molecule of deoxyribose?
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The lone pair of electrons on an oxygen atom in deoxyribose sugar form a dative covalent bond with the phosphorus atom in a condensation reaction a molecule of water is eliminated. A hydrogen is lost from the deoxyribose and and OH group is lost from the phosphate.
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How do bases join to deoxyribose sugar?
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In a condensation reaction , The N atom on the NH group bonds to deoxyribose. An OH group is eliminated from the sugar and a H group is removed from the NH group to form water.
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Why can cytosine behave as a base?
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Lone pair of electrons on the amine ( NH2) group can accept a proton/ hydrogen ion.
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How many hydrogen bonds from between adenine and thymine?
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2 hydrogen bonds
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How many hydrogen bonds from between cytosine and guanine?
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3 hydrogen bonds.
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How is the double- helox model of DNA different to the triple helix model proposed in the past?
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DNA is made up of two strands not three, the phosphate group is on the outside not the inside and the bases face into the centre not the outside.
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Some people believe that DNA fingerprinits of innocent people should be removed from databases, others disagree. Why?
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Some people agree because there is an infringement of personal liability, the fingerprint is not unique it's only a probability. Also the techniques used are not fool proof.
Others disagree because it helps to solve many crimes and it can be used for further research into disease. |
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Why do E-Z isomers form?
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There is no rotation around the C=C bond also there are two different groups on each carbon of a C=C.
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How does changing the composition of double bonds in a polymer to 50% trans and 50% cis affect the crystallinity of a polymer?
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The chains will become less ordered and so the crystallinity will be reduced as the chains are more randomly arranged,
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Why does a polyamide form hydrogen bonds with water but a polyester cannot.
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The amide group in a polyamide forms hydrogen bonds with water molecules. However there is no hydrogen boding in polyesters.
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How does water absorption affect the chain arrangements of polyamides such as nylon-6? How does this affect the glass transition temperature ?
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Water molecules force the chains further apart so the chains are less crystalline. This means that there are weaker intermolecular forces between the chains so the glass transition temperature is lowered.
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How is rust formed?
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If iron is exposed to oxygen and water a series of redox reaction takes place and rust a red-brown precipitate is formed.
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What is the name of rust a red-brown precipitate ?
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Iron (III) hydroxide
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When determining the order of a reaction if a large concentration of acid is used why can it be assumed that the acid does not have an effect on the rate of the reaction?
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The large excess of acid means that their concentrations are practically constant during the reaction, so it has little effect on the rate.
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How can a graph be used to determine that the order of a reaction with respect to a reactant is first order?
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There are two methods. Method one involves calculating the half life ( the time taken for a reaction to half in quantity) from a concentration time graph. If the half life is constant then it's first order.
Method 2 involves finding the rate at different concentrations ( at least 2) if the rate is proportional to the concentration then it's first order. |
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What ways can the rate of a reaction be followed?
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If there is a colour change use a colorimeter to measure the absorbance.
If there is a gas is given off it can be collected in a gas syringe and measured at regular intervals. Measure the pH change if hydrogen ions are used in the reaction. |
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What is meant if a molecule is described as being chiral?
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It has four different groups attached to the carbon atom and the mirror images are not super imposable.
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What is the meaning of the term crystallinity?
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How polymer chains are aligned.
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What is the property of a polymer at a temperature above it's melting temperature?
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The polymer melts as the intermolecular bonds holding the chains are broken using high energy.
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What are the properties of a polymer at temperatures below it's glass transition temperature.
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The polymer becomes brittle because the chains cannot move over each other so they break when a force is applied.
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Why does a blended polymer have a high melting temperature?
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A blended polymer is more crystalline, so intermolecular bonds are stronger and higher energy is needed to separate the chains.
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Why is a polymer made of corn starch considered a 'green' product?
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Its manufactured from a renewable source and it's biodegradable.
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What does the term electronegativity mean?
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The ability for an atom to attract electrons in a covalent bond.
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What is an oxidising agent
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A species that causes something else to be oxidised (loss electrons) but is also reduced in the process ( gains electrons)
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What is a reducing agent?
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A species that causes something to be reduced (gain electrons) but is oxidised in the process
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What is the cell potential of a oxidising agent?
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A strong oxidising agent is more positive as it's reduced.
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What is the cell potential of a reducing agent?
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A strong reducing agent is more negative as it's oxidised to provide electrons.
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What is an acid?
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An acid is a proton donor in an acid in the reverse reaction it acts as a base.
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What is a base?
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A base is a proton acceptor, in the reverse reaction it acts as an acid.
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What is a bidentate ligand?
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It has two lone pairs of electrons that can form dative covalent bonds with a metal cation.
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What is the bond angle formed by a ligand with a coordination number of 6?
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90 degrees
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What is the bond angle formed by a ligand with a coordination number of 2?
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180 degrees
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What is the bond angle formed by a ligand with a coordination number of 4
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109 degrees.
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What type of reaction forms a protein from amino acids?
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condensation reaction
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What reagents and conditions are needed to break down a protein from into it's amino acid?
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moderately concentrated hydrochloric acid heated under reflux.
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How would you use a graph to find the relative rates of reaction at two different temperatures?
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Read it off the graph
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Why does the rate of an enzyme catalysed reaction increases up to 40 degrees then decreases?
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As the temperature rises particles have more kinetic energy so there are more collisions greater than the activation energy. The rate decrease at high temperatures because intermolecular bonds break and the shape of the active site changes.
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Describe how thin layer chromatography is used?
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Draw a pencil line near the bottom of the plate and place one drop of mixture on the line. Place the plate in solvent making sure the line is above the solvent level then cover with a lid. When the solvent nears the top of the plate remove. Locate any spots using UV light or iodine. Calculate the Rf values of the spots and compare with those of the standard.
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How can a carboxylic acid be made from an alcohol?
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Heat under reflux with acidified potassium dichromate (VI).
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How can an aldehyde be made from a primary alcohol?
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Distillation using acidified potassium dichromate (VI)
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What is heating under reflux?
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In heating under reflux the condenser is vertical and the mixture is evaporated and condensed. Also, no reactant or product is lost from the mixture.
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What is the process of distillation?
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In distillation the condenser is horizontal and the mixture is evaporated, condensed and collected. The mixture chemicals are separated.
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What reagent and conditons is used to make an ester from an carboxylic acid and alcohol?
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Concentrated sulfuric acid heated under reflux. Sulfuric acid acts as a catalyst
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What are the advantages of using an enzyme as a catalyst instead of laboratory reagents?
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Reduces the number of steps, increases the atom economy, can be carried out at low temperature reduces and can be reused.
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What happens when an sodium hydroxide is added to an alcohol?
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Nothing as an alcohol does not react with sodium hydroxide.
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What happens when a sodium hydroxide is added to a phenol?
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It reacts with NaOH as it's a weak acid to form a salt that is soluble in water.
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Describe and explain how damage to DNA can result in enzymes becoming less effective for a particular reaction.
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Enzymes are protein with a specific order of amino acids. If the DNA is damaged the primary structure of the protein changes and so does the tertiary structure. The active site is where the reaction with the substrate takes place and an altered active site will not have the correct shape. This means the substrate cant bind to the enzyme to form an enzyme substrate complex.
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Why is a polymer with a glass transition temperature of 9 degrees flexible at room temperature?
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Room temperature is higher than the glass transition temperature which is enough energy to break the intermolecular bonds causing the chains to slide over each other.
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How does adding small side groups to a polymer alter the flexibility?
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The chains in the polymer cannot slide over each other as easily.
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How can a polymer be modified to make it more flexible?
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Add a plasticiser and a copolymer
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At room temperature propene is a gas while propanone is a liquid why?
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Intermolecular bonds in propene is instantaneous dipole - induced dipole, while the intermolecular bonds in propanone is permanent dipole-permanent dipole bonds so more energy is needed to break the bonds in propanone and the intermolecular bonds are stronger.
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What happens if iron(III) chloride in added to an alcohol?
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It remains yellow there is no colour change as there is no phenol group present.
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What happens when an acyl chloride is added to an amine?
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Acylation occurs and one of the hydrogen atoms on the amine NH2 group is substituted for the acyl group to form an N-subistituted amide. HCl is formed.
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Describe how you would carry out a titration with a solution of potassium manganate (VII) and a measured volume of sodium ethanedioate.
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Fill the burette with potassium manganate (VII) solution.
Use a 10 cm cubed pipette to transfer a known volume of sodium ethanedioate into a conical flask and add sulfuric acid. Then slowly add potassium manganate (VII) from the burette into the conical flask while swirling, until a permanent pink colour persists. |
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Why can transition metals such as copper (II) ions increase the rate of a reaction?
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They can act as a homogeneous catalyst so they lower the activation enthalpy. They transition metal reacts to form an intermediate compound and the metal ion can be oxidised or reduced. The intermediate can the react to reform the original transition metal with the original oxidation state at the end of the reaction.
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In order to investigate the order of reaction a student used a large concentration of hydrochloric acid and iodine compared to propanone why?
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During the reaction only the concentration of propanone would change as the concentration of iodine and hydrochloric acid are virtually constant.
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What is a transition metal?
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A metal that can form an ion with a partially filled d orbital.
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What ways can the corrosion of iron be prevented?
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Barrier protection such as painting or oiling prevents oxygen and water coming into contact with iron and steel.
Galvanising steel can be covered with a thin layer of zinc that oxidises. Sacrificial protection attaching blocks of a more reactive metal that reacts instead. |
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What are the outcomes of a clinical trial that is necessary in order for a drug to be marketed?
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The drug has to be non-toxic
It has no harmful or severe side effects It has to work better than standard medicines |
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Suggest why two stereoisomers would be expected to have different activities in the body.
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They have different shapes, so they form enzyme substrate complexes with different enzymes.
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What properties should a solvent have to achieve efficient recrystallisation?
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Solvent should dissolve solute at high temperatures
Solvent should dissolve no solute at low temperatures |
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Describe the process of recrystallisation.
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Heat the impure sample with a minimum amount of hot solvent.
Filter and allow the filtrate to cool in order to crystallise. After crystallisation soluble impurities stay in solution. Filter off the crystals and wash with a minimum volume of cold solvent then dry. |
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Why is the rates of a reaction measured when the amount of reactants used up is small?
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As reactants are used up the rate of the reaction would decrease. The rate measured at the start will be for the initial concentrations.
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Why can a amino (NH2) group acts as a base?
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The nitrogen in the NH2 group has a lone pair of electrons which can accept a hydrogen ion by forming a dative covalent bond.
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What is a zwitterion?
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A dipolar ion that has both a postivie and negative charge.
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What is a primary strtucture?
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The order in which amino acids are joined together.
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What is a secondary structure?
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When a polypeptide chain forms an alpha helix or beta sheet.
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Why is it that at a low concentration of a substrate, the rate of reaction is first order with respect to a the substrate?
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When the substrate is low not all the enzymes active site are filled so an enzyme substrate complex can be formed.
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Why is an enzyme's activity less when the pH is changed?
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Change of pH alters the ionisable groups in the active site. This prevents a substrate from bonding to the active site. At low pH the -NH2 group is protonated and at high pH the -COOH group is deprotonated.
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Why is enzyme activity less when the temperature is high?
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High temperatures break the hydrogen bonds in the tertiary structure and and the shape of the active site changes.
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Why is a reaction no longer first order at high concentrations of a substrate?
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All the active sites are filled so the order becomes zero
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How can a high resolution mass spectroscopy be used to distinguish between compounds that appear to have the same relative molecular mass using a low resolution spectrum?
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It can produce molecular masses correct to 4 decimal places so the masses are not integers. This means that different compounds with the same whole number Mr values would have different Mr values.
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What reagents and conditions are needed to convert an alcohol and carboxylic acid to an ester?
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Heated under reflux with concentrated sulfuric acid.
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