Key Calculations quiz

1. An oxide of nitrogen contains 26% nitrogen and 74% oxygen and has a relative molecular mass of 108. Find the empirical and molecular formulae for the oxide.

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Question 1 of 17

2. State the expression for calculating % yield.

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

% 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)

Question 2 of 17

3. 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 oxygen in so the magnesium fully reacts

To allow carbon dioxide to escape

To stop the crucible heating up too much

To allow some magnesium oxide smoke to escape

Question 3 of 17

4. Calculate the relative formula mass(Mr) of ethanol (C₂H₅OH)

41

45

46

25

Question 4 of 17

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

Endothermic

Exothermic

Depends on the reagents

Depends on the temperature of the surroundings

Question 5 of 17

6. What are the units for amount in Chemistry?

mol/dm³

Moles

Grams

g per 100g of solvent

Question 6 of 17

7. 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

0.68g

17g

68g

Question 7 of 17

8. State the units of molar enthalpy change.

kJ/⁰C

mol/⁰C

kJ/mol

J/⁰C/mol

Question 8 of 17

9. What is the meaning of the term Molar Volume?

The volume of 1 mole of gas at r.t.p (24 dm³ or 24,000 cm³)

The volume of 1 mole of gas at 100 ⁰C (24 dm³ or 24,000 cm³)

The volume of 1 mole of gas at 100 ⁰C (24 cm³ or 24,000 dm³)

The volume of 1 mole of gas at r.t.p (24 cm³ or 24,000 dm³)

Question 9 of 17

10. Use Q=mcΔT and c=4.18J/°C/g. A strip of magnesium is added to a beaker with 200cm³ of copper (II) sulfate. The temperature starts at 21.7°C and rises to a maximum of 23.1°C. What is the total heat energy change?

1170 J

1944 kJ

2.153 kJ

1247 J

Question 10 of 17

11. Complete the following expression: Mᵣ =

mass² / amount (in moles)

mass / amount (in moles)

mass x amount (in moles)

amount (in moles) /mass

Question 11 of 17

12. State the expression for calculating molar concentration

Molar concentration = Amount (in moles)/volume (in cm³)

Molar concentration = Amount (in moles)/volume (in dm³)

Molar concentration = volume (in dm³) / Amount (in moles)

Molar concentration = Amount (in moles) x volume (in cm³)

Question 12 of 17

13. What is meant by the term molecular formula?

A method of calculating the ratios of masses in an equation

A method of calculating the mass needed to make a certain yield in an equation

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 13 of 17

14. What mass of calcium bromide will fully react with 71g of chlorine?

120 g

240 g

200g

480 g

Question 14 of 17

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

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

(12+13)/2 = 12.5

(12x13)/100 = 1.56

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

Question 15 of 17

16. What is the empirical formula of a compound in which 0.48 g of carbon combines with 0.08 g of hydrogen and 0.64 g of oxygen?

C₂H₄O₂

CH₄O

C₄H₂O

CH₂O

Question 16 of 17

17. Describe how to carry out an acid-alkali titration

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

Question 17 of 17

Key Calculations quiz

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