Quantitative Chemistry  [17.12.10]

1.       State and explain what would happen to the pressure of a given mass of gas when its absolute temperature and volume are both doubled.

ANSWER

(Total 3 marks)

 

 

2.       (i)      Crocetin consists of the elements carbon, hydrogen and oxygen. Determine the empirical formula of crocetin, if 1.00 g of crocetin forms 2.68 g of carbon dioxide and 0.657 g of water when it undergoes complete combustion.

ANSWER

(6)

 

(ii)      Determine the molecular formula of crocetin given that 0.300 mole of crocetin has a mass of 98.5 g

ANSWER

(2)

(Total 8 marks)

 

 

3.       0.502 g of an alkali metal sulfate is dissolved in water and excess barium chloride solution, BaCl₂(aq) is added to precipitate all the sulfate ions as barium sulfate, BaSO₄(s). The precipitate is filtered and dried and weighs 0.672 g.

(a)     Calculate the amount (in mol) of barium sulfate formed.

ANSWER

(2)

 

(b)     Determine the amount (in mol) of the alkali metal sulfate present.

ANSWER

(1)

 

(c)     Determine the molar mass of the alkali metal sulfate and state its units.

ANSWER

(2)

 

(d)     Deduce the identity of the alkali metal, showing your workings.

ANSWER

(2)

 

(e)     Write an equation for the precipitation reaction, including state symbols.

ANSWER

(2)

(Total 9 marks)

 

 

4.       Propane and oxygen react according to the following equation.

                        C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

Calculate the volume of carbon dioxide and water vapour produced and the volume of oxygen remaining, when 20.0 dm³ of propane reacts with 120.0 dm³ of oxygen. All gas volumes are measured at the same temperature and pressure.

ANSWER

(Total 3 marks)

 

 

5.       (a)     Define the term isotope.

ANSWER

(2)

 

(b)     A sample of gallium exists as two isotopes, ⁶⁹Ga, relative abundance 61.2%, and ⁷¹Ga, relative abundance 38.8%. Calculate the relative atomic mass of gallium.

ANSWER

(1)

(Total 3 marks)

 

 

6.       Some vaporized magnesium is introduced into a mass spectrometer. One of the ions that reaches the detector is ²⁵Mg⁺.

(a)     Identify the number of protons, neutrons and electrons in the ²⁵Mg⁺ ion.

ANSWER

(1)

 

(b)     State how this ion is accelerated in the mass spectrometer.

ANSWER

(1)

 

(c)     The ²⁵Mg²⁺ ion is also detected in this mass spectrometer by changing the magnetic field. Deduce and explain, by reference to the m/z values of these two ions of magnesium, which of the ions ²⁵Mg²⁺ and ²⁵Mg⁺ is detected using a stronger magnetic field.

ANSWER

(2)

(Total 4 marks)