Chemistry - The nature of substances and chemical reactions - chemical equations and calculations Flashcards
Where does the reactant and the product go in a word equation?
Reactants : arrow points away
Product : arrow points towards
What are the four state symbols?
(s) Solid
(l) Liquid
(g) Gas
(aq) Aqueous (dissolved in water)
How do you find the relative formula mass (Mr) of a compound?
You add together the relative atomic mass values (Ar values) for all the atoms in its formula.
Why isn’t it always possible to get the entire calculated amount of product from a reaction?
-reversible reactions may not be completed
-some product may be lost when it is removed from the reaction mixture
-some of the reactants may react in an unexpected way
How do you work out the percentage mass of a compound?
% mass = (Total Ar of the element ÷ Mr of the compound) × 100
How do you calculate the percentage yield?
Percentage yield = mass obtained/expected mass x 100
Why might percentage yield of a product be less than 100%?
loss when filtering
loss when evaporating
loss when transferring liquids
not all reactants reacting to make product
3.2 g of sulfur reacts with oxygen to produce 6.4 g of sulfur oxide. What is the formula of the oxide?
3.2 g of sulfur reacts with oxygen to produce 6.4 g of sulfur oxide.
1 Write the element symbols (S) [O]
2 Write the masses (3.2 g) [6.4 g – 3.2 g = 3.2 g]
3 Write the Ar values (32) [16]
4 Divide masses by Ar (3.2 ÷ 32 = 0.1) [3.2 ÷ 16 = 0.2]
5 Divide by the smallest number (0.1 ÷ 0.1 = 1) [0.2 ÷ 0.1 = 2]
6 Write the formula ([ SO2 ])
How do you convert the empirical formula to the molecular formula?
-Add up the atomic masses of the atoms in the empirical formula.
-Divide the Mr by the mass
-multiply the numbers in the empirical number by the outcome.
How do you calculate the number of moles?
number of moles = mass ÷ relative formula mass (Mr)
What is Avogadro’s constant?
1 mole of a substance contains 6.022 × 10^23 atoms or molecules.
