Key Calculations quiz

1. Complete the following expression: Mᵣ =

mass² / amount (in moles)

mass / amount (in moles)

amount (in moles) /mass

mass x amount (in moles)

Question 1 of 17

2. Use Q=mcΔT and c=4.18J/°C/g. 25cm³ of sulfuric acid is put into a boiling tube. The starting temperature is 21°C. A spatula of iron filings is added. After a while the temperature reaches 33°C. What is the total heat energy change?

1254 J

3383 J

2153 J

2.153 kJ

Question 2 of 17

3. A compound that contained 24.24% Carbon. 4.04% Hydrogen and 71.72% Chlorine and has a relative molecular mass of 99. Calculate the empirical formula and the molecular formula.

Empirical formula is C₂H₄Cl₂. Molecular formula is C₂H₄Cl₂

Empirical formula is C₂H₄Cl₂. Molecular formula is CH₂Cl

Empirical formula is CH₂Cl. Molecular formula is CH₂Cl

Empirical formula is CH₂Cl. Molecular formula is C₂H₄Cl₂

Question 3 of 17

4. 1.170 g of CoCl₂.xH₂O gave a residue of 0.641 g on heating. Find x.

3

5

6

7

Question 4 of 17

5. What volume does 3 moles of carbon dioxide gas occupy (at rtp)?

8 dm³

8 cm³

72 dm³

72 cm³

Question 5 of 17

6. Name this piece of lab equipment

funnel

burette

measuring cylinder

pipette

Question 6 of 17

7. A sample of carbon contained 98.90% carbon-12 and 1.10% carbon-13. Calculate the relative atomic mass of carbon

((13x98.90)+(12x1.10))/100 = 12.99

((12x98.90)+(13x1.10))/100 = 12.01

(12x13)/100 = 1.56

(12+13)/2 = 12.5

Question 7 of 17

8. State the units of molar enthalpy change.

kJ/⁰C

mol/⁰C

J/⁰C/mol

kJ/mol

Question 8 of 17

9. What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?

88g

44 g

176 g

24 g

Question 9 of 17

10. A graph shows the solubility of sodium chloride in water at 50°C is 34g/100g. At that temperature, what mass of sodium chloride will dissolve in 200g water?

0.34g

17g

0.68g

68g

Question 10 of 17

11. 25 cm³ of sodium chloride solution has a concentration of 0.5 mol/dm³. What amount of sodium chloride does it contain?

0.05 mol

12.5 mol

1.25 mol

0.0125 mol

Question 11 of 17

12. What is meant by the term empirical formula?

A method of calculating the ratios of masses in an equation

A chemical formula that shows the simplest ratio of the numbers of atoms in a compound

Baby food for emperors

A chemical formula that shows the actual numbers of the different types of atoms in a molecule

Question 12 of 17

13. Calculate the relative formula mass(Mr) of ammonium nitrate (NH₄NO₃)

66

48

80

45

Question 13 of 17

14. Assuming bond energies in kJ/mol: H-C 412, C-C 348, O-H 463, C-O 360, C=C 612. Calculate the molar enthalpy change for the reaction: ethanol → ethene + water

-45 kJ/mol (Some workings as follows. Breaking bonds 1583 kJ/mol. Making bonds 1487/mol. Making - breaking = 1487-1583 = -96 kJ/mol)

-45 kJ/mol (Some workings as follows. Breaking bonds 3231 kJ/mol. Making bonds 3186kJ/mol. Making - breaking = 3186-3231 = -45 kJ/mol)

+96 kJ/mol (Some workings as follows. Breaking bonds 1583 kJ/mol. Making bonds 1487/mol. Breaking - making = 1583-1487 = +96 kJ/mol)

+45 kJ/mol (Some workings as follows. Breaking bonds 3231 kJ/mol. Making bonds 3186kJ/mol. Breaking - making = 3231-3186 = +45 kJ/mol)

Question 14 of 17

15. What is the meaning of the word mole in Chemistry?

A mole is a small burrowing mammal

Moles are the units for amount of substance. (1 mole is 10 g of a substance)

Moles are the units for amount of substance. 1 mole of a substance is its relative formula mass in grams (e.g. 1 mole of magnesium is 24 g)

Moles are the units for amount of substance. 1 mole of an element is its atomic number in grams (e.g. 1 mole of magnesium is 12 g)

Question 15 of 17

16. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid lifted from time to time?

To allow some magnesium oxide smoke to escape

To allow carbon dioxide to escape

To stop the crucible heating up too much

To allow oxygen in so the magnesium fully reacts

Question 16 of 17

17. State the expression for calculating % yield.

% yield = (theroretical amount of products/actual amount of products) x 100

% yield = (actual amount of products/theoretical amount of products)

% yield = (actual amount of products/theoretical amount of products) x 100

% yield = (theroretical amount of products/actual amount of products)

Question 17 of 17

Key Calculations quiz

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