Reacting MassesOxford AQA IGCSE Chemistry: Flashcards

Card 1 of 120 of 12 known

Question

What does the law of conservation of mass state?

Tap or press Space to reveal

Tap card or press Space to flip

See all 12 cards

What does the law of conservation of mass state?: No atoms are lost or made during a chemical reaction, so the total mass of products equals the total mass of reactants.
What is the first step in calculating a reacting mass?: Write the balanced symbol equation for the reaction.
How do you convert a known mass into moles?: n = mass ÷ Mr.
How do you convert moles of a substance back into mass?: mass = n × Mr.
What does the mole ratio in a balanced equation come from?: The large numbers written in front of each formula in the balanced equation.
In the equation 2Mg + O2 → 2MgO, what is the mole ratio of Mg to MgO?: 1:1 (2 mol Mg produces 2 mol MgO).
Give one reason why an actual yield might be lower than the calculated (theoretical) yield.: The reaction may not go to completion, product may be lost during separation, or reactants may undergo unexpected side reactions.
State symbols: what does (aq) mean?: Dissolved in water (aqueous).
6 g of magnesium (Ar = 24) reacts completely. How many moles of magnesium is this?: 6 ÷ 24 = 0.25 mol.
Why must you convert to moles rather than working directly with masses when using a balanced equation?: Because the balanced equation gives ratios of moles of particles, not ratios of mass.
What must be true of a symbol equation before it can be used for reacting mass calculations?: It must be correctly balanced, so the number of atoms of each element is equal on both sides.
Name the four state symbols used in chemical equations.: (s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved in water).