Key Calculations quiz

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

66

45

80

48

Question 1 of 17

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

44 g

24 g

88g

176 g

Question 2 of 17

3. What are the units for amount in Chemistry?

g per 100g of solvent

Grams

Moles

mol/dm³

Question 3 of 17

4. State the expression for calculating molar volume of a gas.

Molar volume = amount (in grams) x 24 dm³ (or 24,000 cm³)

Molar volume = amount (in moles) x 24 dm³ (or 24,000 cm³)

Molar volume = amount (in moles) / 24 dm³ (or 24,000 cm³)

Molar volume = amount (in grams) / 24 dm³ (or 24,000 cm³)

Question 4 of 17

5. What is the empirical formula of an alcohol with the analysis; 52.2% C, 13.0% H and 34.8% O?

CH₆O

C₂H₆O₂

C₂H₆O

C₂H₃O

Question 5 of 17

6. 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 50g water?

0.17g

17g

68g

0.68g

Question 6 of 17

7. A sample of bromine contained the two isotopes in the following proportions: bromine-79 = 50.7% and bromine-81 = 49.3%. Calculate the relative atomic mass of bromine

((79x50.7)+(81x49.3))/100 = 79.99

(81x79)/100 = 63.99

((81x50.7)+(79x49.3))/100 = 80.01

(81 + 79)/2 = 80

Question 7 of 17

8. 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) x 100

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

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

Question 8 of 17

9. In a chemical reaction, the overall molar enthalpy is -87 kJ/mol. Is this reaction exothermic or endothermic?

Exothermic

Depends on the reagents

Depends on the temperature of the surroundings

Endothermic

Question 9 of 17

10. State the units of molar enthalpy change.

mol/⁰C

kJ/⁰C

kJ/mol

J/⁰C/mol

Question 10 of 17

11. What is meant by the term empirical formula?

A method of calculating the ratios of masses in an equation

Baby food for emperors

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

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

Question 11 of 17

12. Name this piece of lab equipment

measuring cylinder

pipette

burette

gas syringe

Question 12 of 17

13. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is the crucible is cooled, weighed, reheated, cooled, re-weighed, and so on?

To ensure all the magnesium oxide to escape

To allow any water to escape

To make sure the mass is still going down so the magnesium is still reacting

To make sure a constant mass has been reached and there is no more magnesium left to react

Question 13 of 17

14. 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 CH₂Cl

Empirical formula is CH₂Cl. Molecular formula is CH₂Cl

Empirical formula is C₂H₄Cl₂. Molecular formula is C₂H₄Cl₂

Empirical formula is CH₂Cl. Molecular formula is C₂H₄Cl₂

Question 14 of 17

15. Complete the following expression: Mᵣ =

mass x amount (in moles)

mass / amount (in moles)

amount (in moles) /mass

mass² / amount (in moles)

Question 15 of 17

16. A beaker of 1.5 mol/dm³ calcium chloride solution contains 0.3 mol of calcium chloride. What is the volume of the solution?

4.5 dm³

0.2 dm³

0.002 dm³

0.45 dm³

Question 16 of 17

17. Use Q=mcΔT and c=4.18J/°C/g. A spatula of sodium fluoride is put into a boiling tube with 25cm³ of water. The temperature drops from 22.0°C to 18.6°C. What is the total heat energy change?

1944 kJ

355 kJ/mol

355 J

1944 J

Question 17 of 17

Key Calculations quiz

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