Chem Lab Exam

Front 1

In the reaction below, what is the mole ratio between Mg(s) and H2(g)

Mg + 2HCl --> MgCl2 + H2

Back 1

the mole ratio is 1:1 between Mg and H2

Front 2

Is the H2 gas that is collected in the experiment pure or impure? why or why not?

Back 2

it is impure as it will contain water vapour or H2O(g)

Front 3

What value did we not need to record for this experiment? (experiment 2 with H2 gas)

Back 3

we didn't need Time

Front 4

Why mustn't we overfill the reactor? What capacity must you not supersede?

Back 4

You must not fill the reactor beyond 80% capacity. this will cause the pressure to become too high.

Front 5

In light of the fact that we cannot fully fill the reactor, what formula is used to correct pressure?

Back 5

Ph2 = Patm -- Ph2o

Front 6

what does Patm represent?

Back 6

Patm is the atmospheric pressure of the room given to the student by the teacher

Front 7

what is PH2O

Back 7

PH2O is obtained by looking at the temperature of the room, and using the chart to find the corresponding pressure in KPA

Front 8

How was it determined how much Magnesium was needed for the experiment

Back 8

step 1: take the pressure given in the lab manual and subtract the KPA that corresponds with room temp.

step 2: the formula PV = NRT was rearranged for "n" and then once n was found you multiplied by molar mass to get grams.

Front 9

What happens if there were an undetected air bubble in the reaction?

Back 9

an undetected air bubble would result in the volume being too high, and an "actual" yield value that is erroneously high.

The increase in V causes an increase in N and ultimately a number thats too high

Front 10

What happens if not enough HCL was added to the experiment

Back 10

a decreased volume of HCL will mean there actual yield value is too low.

Front 11

How do you calculate the actual yield

Back 11

step 1: use n = PV/rT

step 2: put corrected pressure, volume in L, 8.314, and temp in K from table into formula

Front 12

how do you calculate theoretical yield

Back 12

The mass is found by taking moles and multiplying by molar mass

You do not have the mass of H2, so take the moles of Mg you calculated and multiply it by (2)(molar-mass of hydrogen)

While Mg and H2 do have a 1:1 ratio, the molar mass of hydrogen doesn't account for the fact that H2 gas is diatomic, and must be doubled.

Front 13

How do you find the percent yield

Back 13

A

-- x100%

T

Front 14

Experiment 3 (hit next)

Back 14

--

Front 15

In this hess's law experiment, why can't we calculate H3 and H4 on our own

Back 15

they involve toxic gases

Front 16

why is the temp of ammonia different from that of HCl

Back 16

it is slightly LOWER as it is constantly evaporating

Front 17

What type of system is a calorimeter

Back 17

it is isolated

Front 18

What type of reaction is this

Back 18

acid/base neutralization of a salt

Front 19

how do you find the mass of total calorimeter content in part a

Back 19

you would take the two chemicals, HCL, and NH3 and add their masses together

(which can be found by adding their volumes together since density is 1g/1ml)

Front 20

how do you find the mass in part B

Back 20

take the mass of NH4Cl obtained by weighing by difference, and add this too the volume of of water

Front 21

how do you find the limiting reagent?

Back 21

Out of the two reactants in part A, the limiting reactant can be found by taking the moles of HCl and NH4 respectively and dividing by the molar coefficients.

In this experiment, the LR is HCl

Front 22

Once q is found, how is Calculated enthalpy of reaction found in part A and B

Back 22

in part A, the Q must by switched to KJ and then divided by the moles of the limiting reagent

in part B, the Q must be switched to KJ and divided by the moles of NH4Cl, the only chemical

Front 23

How do you find delta H 5

Back 23

by adding the values of delta H 1-4. But some of them may have to be manipulated in accordance with Hess's law

Front 24

Experiment 7

Back 24

switch slide

Front 25

What color signifies that you have reached the end point

Back 25

light pink

Front 26

Explain the common ion effect

Back 26

the presence of a common ion decreases solubility

Front 27

define a saturated solution

Back 27

a saturated solution is one that contains a max concentration of the solute it is dissolving. It is a solvent that has reached is solubility limit

Front 28

What are the steps of prepping the biuret for use

Back 28

1. take biuret off stand

2. rinse buret with H2O

3. Rinse biuret with titrant

4. fill buret with titrant

5. remove air bubbles

6. take initial reading

Front 29

What are the steps of putting away a buret

Back 29

1. Drain remaining titrant into a waste beaker

2. Rinse the Buret thoroughly with distilled water

3. Dump waste beaker into aqueous waste

4. flip buret upside-down with stopcock loose and open

Front 30

If you are titrating with HCL as a titrant, how do you find the volume of HCL

Back 30

take the final buret reading and subtract initial

Front 31

how do you covert the volume of HCl into moles Hcl

Back 31

molarity (given) times Hcl volume in litres

Front 32

if your moles of HCL are 0.000402 how do you find the moles of Hydroxide

Back 32

in this experiment there are 2HCL molecules for every one Ca(OH)2 molecule.

2HCL : 2(OH)

so, you would take the 0.000402 and divide by 0.01L because there is 10ml of Ca(OH)2

Front 33

once the concentration of OH is found how is the concentration of Ca(OH)2 and Ca found

Back 33

well if 2OH is 0.0402 then 1Ca(OH)2 and 1 Ca is 0.0201

Front 34

how is the experimental solubility calculated

Back 34

1. you take the moles of HCL and convert them tomes of CaOH2 by dividing by 2

2. once you do this, you multiply by the molar mass and divide by 0.01L

Front 35

How is mean calculated?

Back 35

take the values that are asked about, and divide by n (number of values)

Front 36

how is STD DEV found

Back 36

well, you take the number and subtract the mean. then you take this number and square it

you do this again for all numbers you are comparing

add all answers together and divide by n-1

then take square root

Front 37

how do you calculate RSD

Back 37

take the standard deviation and divide by mean

Front 38

Why is it that the KSP of all trials are similar

Back 38

because the only thing that changes KSP is TEMPERATURE

Front 39

how does the presence of a strong acid affect the sollubility value

Back 39

it increases it

Front 40

how does the presence of NaOH affect the KSP of CAOH2?

Back 40

it lowers the solubility due to the common ion effect

Front 41

how would a soluble compound like KNO3 affect the solubility

Back 41

it wouldn't change it

Front 42

Experiment 8

Back 42

hit next

Front 43

what is the indicator solution in this lab

Back 43

starch indicator solution

Front 44

what is the oxidizing agent in this experiment? what is its role in bleach?

Back 44

CLO- or hypochlorite, it removes stains

Front 45

What is the molar ratio of Na2S2O3 (sodium thiosulphate) to Hypochlorite (ClO-)

Back 45

2:1

Front 46

if you are told to weigh and empty flask and then weigh a flask with bleach in it, how do you obtain the mass of bleach

Back 46

weighing by difference

Front 47

how are the moles of thiosulphate found

Back 47

Molarity times Litres

Front 48

how are the moles of CLO found

Back 48

divide by 2

Front 49

how is the mass of sodium hypochlorite found

Back 49

take the moles of CLO and multiply by molar mass of sodium hypochlorite

Front 50

What is the relationship between species oxidized and the reducing agent

Back 50

they are the same

Front 51

What is the relationship between species reduced and oxidizing agent

Back 51

they are the same

Front 52

What must be remembered when determining oxidizing agents etc

Back 52

you can only name the reactants in the equation not products, meaning the "Reducing agent" for a reaction is the reactant.

Front 53

If a new bottle of clorox bleach (that is 100g) is 7% sodium hypochlorite

what is the Ph? The KA is 3.5x10-8 and the bleaches density is 1.07 g/ml

Back 53

1) the 100g sample is 7% potent so that means there are 0.07g or (7/100)g of NaClO.

2) Divide mass by molar mass (74.44) to get moles

3. mutpliple the moles/g by the density (1.07g/ml) to get moles per ml

4. change this to moles per litre by multiplying your answer by 1000

5. next, turn the Ka into the Kb using the Ka x Kb = Kw equation

6. Finally, create an ice chart for the reaction of ClO- + H2O --> HCLO + OH where the Eq'm concentration is (answer for 4 subtract x) and the products make x^2.

7. use KB to solve for x. do -log x to find ph

Front 54

THE END

Back 54

THE END