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25 Cards in this Set
- Front
- Back
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What is the definition of a mole? |
The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12. |
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What is the relative atomic mass? |
Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12. |
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What is the definition of relative molecular mass? |
Relative molecular mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12. |
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What is the formula to calculate moles? |
Moles = mass ÷ Mr |
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What is the ideal gas equation? |
PV = nRT P = Pressure (Pa) V = Volume (m³) R = 8.31 T = Temperature (K) |
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What is the formula to calculate the concentration for solutions? |
Concentration = moles ÷ volume |
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How do you calculate the number of particles? |
No. of particles = moles of substance (in mol) × Avogadro’s constant |
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How do you calculate density? |
Density = mass ÷ volume |
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What is the definition of the empirical formula? |
An empirical formula is the simplest ratio of atoms of each element in the compound. |
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What is the general method to work out the empirical formula? |
Step 1: Divide each mass (or % mass) by the atomic mass of the element. Step 2: For each of the answers from Step 1 divided by the smallest one of those numbers. Step 3: Sometimes the numbers calculated in Step 2 will need to be multiplied up to give whole numbers. |
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What other types of data can the method used to find the empirical formula find? |
Masses of each element in the compound. Percentage mass of each element in the compound. |
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What is the definition of a molecular formula? |
A molecular formula is the actual number of atoms of each element in the compound. |
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How do you work out the relative molecular mass? |
Work out how many times the mass of the empirical formula fits into the Mr. |
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What is a solution? |
A solution is a mixture formed when solute dissolves in asolvent. |
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How can molar concentration be measured? |
Concentration = moles ÷ volume |
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How do you prepare a solution? |
Weigh the sample bottle containing the required mass of solid on a 2 dp balance. Transfer to beaker and reweigh sample bottle. Record the difference in mass. Add 100cm^3 of distilled water to the beaker. Use a glass rod to stir to help dissolve the solid. Pour solution into a 250cm^3 graduated flask via a funnel. Rinse beaker and funnel and add washings from the beaker and glass rod to the volumetric flask. Make up to the mark with distilled water using a dropping pipette for last few drops. Invert flask several times to ensure uniform solution. |
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How do you dilute a solution? |
Pipette 25cm^3 of original solution into a 250cm^3 volumetric flask. Make up to the mark with distilled water using a dropping pipette for last few drops. Invert flask several times to ensure uniform solution. |
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How do you calculate the concentration of the diluted solution? |
new diluted concentration = original concentration x (original volume ÷ new diluted volume) |
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What are the potential errors whilst using a gas syringe? |
Gas escapes before bung inserted. Syringe sticks. Some gases like CO2 or SO2 are soluble in water so the true amount of gas is not measured. |
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How do you calculate the percentage yield? |
percentage yield = (actual yield ÷ theoretical yield) x 100 |
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How do you calculate percentage atom economy? |
percentage atom economy = (Mass of useful products ÷ Mass of all reactants) x 100 |
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How do you carry out a titration? |
Rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water). Pipette 25 cm3 of alkali into conical flask. Add acid solution from burette. Make sure the jet space in the burette is filled with acid. Add a few drops of indicator and refer to colour change at endpoint Phenolphthalein, pink (alkali) to colourless (acid): endpoint is when pink colour just disappears. Use a white tile underneath the flask to help observe the colour change. Add acid to alkali whilst swirling the mixture and add acid dropwise at endpoint. Note burette reading before and after addition of acid. Repeat titration until at least 2 concordant results are obtained - two readings within 0.1 of each other. |
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How do you calculate the uncertainty of a reading? |
The uncertainty of a reading is at least ±0.5 of the smallest scale reading. This happens after one judgment. |
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How do you calculate the uncertainty of a measurement? |
The uncertainty of a measurement is at least ±1 of the smallest scale reading. This happens after two judgements. |
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How do you calculate % uncertainty? |
% uncertainty = ± (uncertainty ÷ Measurement made on apparatus) × 100 |
