C4- Chemical Calculations Flashcards
How do you work out the relative formula mass of a compound?
1) Adding up the relative atomic masses in the ratio shown by its formula.
How are the masses of atoms compared?
1) The masses of atoms are compared by measuring them relative to atoms of carbon.
Explain what one mole of any substance is
How can you work out the number of moles?
Explain what Avogadros constant is.
1) One mole of any substance is its relative formula mass (in grams).
2) Number of moles= mass(g)/Mr
3) Avogadro’s constant is 6.02x10^23
In a chemical reaction, what is the name of the reactant that gets used up first?
What does this determine?
1) The reactant that gets used up first is called the ‘Limiting reactant’
2) The Limiting reactant determines the amount of product formed in a chemical reaction.
What does the yield of a chemical reaction describe?
What does percentage yield tell you?
1) The yield of a chemical reaction describes how much product is made.
2) Percentage Yield of a chemical reaction tells you how much product is made compared with the maximum amount that could have been made (100%)
What does the Law of Conservation state?
1) The Law of Conservation states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants
Why might some reactions appear to have changed in mass? How can this be explained?
1) Some reactions may appear to have changed in Mass however this can be explained because a reactant or product is a gas and its mass has not been taken into account.
What is the equation for percentage yield?
1) Percentage Yield = actual mass of product produced
———————————— X100
Maximum theoretical mass of product possible
Explain some of the factors that can affect the yield of a chemical reaction.
1) Factors affecting the yield of a chemical reation include:
- Product being left behind in the apparatus.
- Reversible reactions not being fully completed
- Some reactants may produce unexpected reactions
- Losses in separating the products from the reaction mixture.
Give the equation for percentage atom economy.
1) Percentage Atom Economy =
relative formula mass of desired product from equation
————————————————————- x 100
Sum of the relative formula masses of rectants from the equation
Why is it important to maximise atom economy in industrial processes?
1) It is important to maximise atom in industril processes to conserve the Earth’s resources and minimise pollution.
Give the formula for concentrattion.
1) Concentration (g/dmˆ3) =
Amount of solute (g)
—————————– x1000
Volume of solution (cmˆ3)
Give 2 ways in which you can increases the concentration of an aqueous solution.
1) Adding more solute and dissolving it in the same volume of its solution.
2) Evaporating off ome of the water from the solution so that you have the same mass of solute in a smaller volume of solution.
What is titration used for?
1) Titration is used to measure accurately what volumes of acid and alkali react together completely.
Give the method for Carrying out a Titration (RP)
1) Collect the acid in a beaker and label it.
2) Rinse the burette with ditilled water and then with some of the acid.
3) Fill a burette with the acid beyond the zero mark, then let the solution run out until the bottom of the meniscus is exatly on the zero mark.
4) Collect your alkali in another beaker.
5) Rinse the pipette with distilled water and then with the acid.
6) Use the pipette and pipette filler to transfer 25.0cm3 of the alkali into a clean dry conical flask.
7) Add 3-4 drops of the indicator into the flask and swirl. Place the conical flask on the white tile directly below the burette.
8) Record the initial burette reading.
9) Add the acid to the alkali in small amounts at a time. Swirl the flask after every titration. Continue until the indicator goes to colourless.
10) Repeat accurately by adding the acid drop wise near thhe end point. Record the final and initial burette readings in the apporpriate column in your table.
