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level: Calculations in Chemistry

Questions and Answers List

level questions: Calculations in Chemistry

QuestionAnswer
How is a solution formed?when a solute dissolves in a solvent
What's the formula for concentrationconcentration (g/dm^3) = mass of solute (g) ÷ volume (dm^3)
How can concentration be increased?1) by dissolving more solute in a given volume of solution - this increases the mass of the solute 2) by allowing some of the solvent to evaporate - this decreases the volume of the solution
What's the equation linking No. of Particles, Avogadro's constant & amount(mol)?No. of particles = Avogadro's constant × amount of substance in mol
What's the equation linking Mass, Rfm & amount(mol)?Mass = relative formula mass × amount
In a balanced equation, what shows the amount(mol) of products and reactants?The coeficient (number infront of formulae). No coefficient means 1 mol
What is a limiting reactant?The reactant that is all used up. This is what The mass of product formed in a reaction depends on
What's the excess?the reactant that is left over
12 g of magnesium reacts completely with excess hydrochloric acid to form magnesium chloride and hydrogen: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) Calculate the maximum mass of hydrogen that can be produced. (Ar of Mg = 24, Mr of H2 = 2)Amount of magnesium = mass ÷ rfm Amount of magnesium = 12/24 = 0.5 mol Looking at the equation, 1 mol of Mg forms 1 mol of H2, so 0.5 mol of Mg forms 0.5 mol of H2 Mass of H2 = Mr × amount = 2 × 0.5 = 1 g
What's the equation for concentration?Concentration(mol/dm^3) = amount of solute(mol) ÷ volume (dm^3) REMEMBER: × by 100 to go from dm^3 to cm3
How do you convert between mol/dm^3 to g/dm^3 (vice versa)?'×' by the rfm (to go from g/dm^3 to mol/dm^3 '÷' by the rfm)