Unit 1-Reaction Quantities
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What is meant by the gram formula mass (GFM)?
The mass of one mole of a substance
How do you calculate the GFM of a compound?
Add together the relative atomic masses of all atoms in the formula
What is the GFM of CO2?
12 + (2 × 16) = 44 g mol⁻¹
What is the formula linking mass, moles and GFM?
Number of moles = mass ÷ GFM
How many moles are in 25 g of CaCO₃ (GFM = 100)?
n = m ÷ GFM 25 ÷ 100 n = 0.25 moles
What is the mass of 0.25 moles of butane (C4H10) GFM is 58
mass = number of moles x GFM mass = 0.25 x 58 mass = 14.5 g
What is the formula linking concentration, moles and volume?
number of moles = concentration × volume
How many moles are in 400 cm³ of 0.2 mol l⁻¹ NaOH?
Number of moles = concentration x volume Convert volume to litres by dividing by 1000 n = 0.2 x 0.4 n= 0.08 moles
What is the concentration when 0.75 moles is dissolved in 500 cm-3?
Concentration = number of moles ÷ volume. Convert volume into litres by dividing by 1000. c = 0.75 ÷ 0.5 = 1.5 mol l-1 Concentration = 1.5 mol l-1
What volume is needed for 1.2 moles of solute in a 0.6 mol l-1 solution?
Volume = number of moles ÷ concentration V = 1.2 ÷ 0.6 = 2.0 l
What mass of magnesium is needed to produce 0.8 g of hydrogen gas? Mg + 2HCl → MgCl2 + H2
Moles of hydrogen = m ÷ GFM n = 0.8/2 = 0.4 moles ratio is 1:1 therefore also 0.4 moles of magnesium Mass of magnesium = n x GFM m = 0.4 x 24.5 m = 9.8g
What mass of oxygen is produce when 85g of hydrogen gas decomposes? 2H2O2 → 2H2O + O2
Moles of hydrogen peroxide = m ÷ GFM n = 85/34 = 2.5 moles ratio is 2:1 therefore 1.25 moles of oxygen Mass of oxygen = n x GFM m = 1.25 x 32 m = 40 g
What mass of copper(II) sulfate is produced when 8.0 g of copper(II) oxide reacts completely? CuO + H2SO4 → CuSO4 + H2O
Moles of CuO = m ÷ GFM n = 8/79.5 = 0.1 moles ratio is 1:1 therefore also 0.1 moles of CuSO4 Mass of copper sulfate = n x GFM m = 0.1 x 159.5 m =15.95 g
How do you calculate percentage by mass?
% by mass = (mass of element in 1 mole ÷ GFM) × 100
What is the % of magnesium in magnesium oxide (MgO)?
Mg has GFM of 24 g mol-1 . MgO has GFM = 40 g mol-1 % by mass = (24 ÷ 40) × 100 = 60%
What is the % of nitrogen in ammonium nitrate (NH4NO3)?
8N has GFM of 14 g mol-1 . There are two nitrogen in compound. (NH4NO3) has GFM = 80 g mol-1 % by mass = (24 ÷ 80) × 100 = 35%