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Quantitative Chemistry Flashcards

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1
Q

What is meant by a mole?

A

the “mole” is a unit that measures the number of atoms in a sample
1 mole = 6x1023 (Avogadro’s number)

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2
Q

What is the equation for mole?

A

Moles = mass/ Mr

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3
Q

How do you calculate the percentage by mass of an element in compound?

A

[(Ar of element x no. atoms)/ Mr of compound] x 100

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4
Q

What is the empirical formula?

A

The empirical formula of compound is the formula in the smallest possible whole-number ratio of each element present in the compound

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5
Q

How do you find the empirical formula of a compound from the % composition of mass of its elements?

A
  • Write out the experimental mass of each element
  • Divide each mass by the Ar values
  • Divide each by the smallest number in the row
  • Multiply to get whole numbers if necessary
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6
Q

What is the molar formula?

A

A multiple of the empirical formula

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7
Q

How do you work out the molecular formula from the empirical formula of a compound?

A
  • Work out the empirical formula mass (Mr of the empirical formula)
  • divide the Mr of the compound by the empirical formula mass
  • Multiply the no. of atoms of each element in the empirical formula by the answer
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8
Q

How do you use a balanced equation to calculate the masses of reactants or products?

A
  1. Write the balanced equation
  2. Use the balanced equation to see the ratio of moles that react
  3. Use the equation mass = moles x Mr to calc mass from the moles/ Mr
    (to check the answer is right, make sure the mass of reactants=mass of products)
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9
Q

How do you use the masses of reactants/ products to balance an equation?

A
  1. Calculate the RFM/Mr for each substance
  2. Calculate the moles of each substance using the equation
  3. Simplify the moles ratio to simple whole numbers
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10
Q

When you are given the masses of reactants, how can you use this to find the limiting reactant?

A
  1. Calculate the Mr of the reactants
  2. Work out the moles from the mass and Mr- this is how many moles are PRESENT
  3. Write out the mole ratio from the balanced equation- this is how many moles are NEEDED TO REACT
  4. Whichever reactant has less moles than what is needed to react, is LIMITING
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11
Q

How would you find the mass of a product from a reaction, where you are only given the mass of the reactants?

A
  1. Calculate the Mr of the reactants
  2. Work out the moles from the mass and Mr- this is how many moles are PRESENT
  3. Write out the mole ratio from the balanced equation- this is how many moles are NEEDED TO REACT
  4. Whichever reactant has less moles than what is needed to react, is LIMITING
  5. Use the moles PRESENT of the limiting reactant to calculate the moles of the product (use mole ratio)
  6. Calculate the Mr of the product
  7. Work out the mass of the product from the moles and Mr
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12
Q

How can you use the ideal gas equation to work out the moles from the volume of a gas?

A

ideal gas equation=pv=nRT

  • the volume of a gas depends on the conditions of temp and pressure not the IDENTITY of the gas
  • When gasses are measured under the same conditions of temp and pressure
  • the vol = the no. of moles
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13
Q

what is meant by the “molar volume”

A

When the temperature and pressure of a gas is given, there is a specific value for the amount of gas in that given volume=
“molar gas”

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14
Q

What is the specific value of the molar gas at room temp and pressure?

A

24dm3

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15
Q

What expression represents the relationship between the molar gas volume, the volume of the gas and the number of moles of the gas?

A

No of moles of gas = volume/ molar volume

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16
Q

What are the 2 equations used to calculate the concentration of a solution? what are the 2 different units used?

A 
conc = mass of solute/vol of solution
UNITS: g dm-3
OR 
conc = mol/vol
UNITS: mol dm-3
17
Q

How would you determine the volume of concentrated solution you would need to give to get a more dilute solution? (e.g, in acid-base titrations)?

A
  1. Calculate the number of moles you would have in the dilute solution you want to acquire
  2. Then divide the concentration of the original/ more concentrated solution by this mole
  3. This would give you the volume of the concentrated solution required to make the dilute solution
18
Q

How do you convert g dm-3 to mol dm-3

E.g, what is the conc of 20g dm -3 of sodium hydroxide in mol dm-3?

A
  • 20g dm-3 means there are 20g of solution in 1 dm3 of that solution
    1. Calculate the number of moles in 1 dm3 of that solution
    2. moles = mass/ Mr
    3. Mr of of NaOH = 40
    4. moles = 20/40 = 0.5
    5. so we know there are 0.5 moles in 1dm3 of solution
    i. e. the conc = 0.5 mol dm-3
19
Q

What is meant by the term “saturated solution”?

A

A solution in which no more solute will dissolve at a given temperature

20
Q

What affect does temperature have on the solubility of gases?

A

-As the temp INCREASES the solubility of gases DECREASES

21
Q

How can a solubility graph be used to calculate the mass of a salt that will precipitate a specific mass of a solution at a certain temp change?

A
  1. Find out how much of the salt will saturate the solution at the original temp
  2. Find out how much of the salt will saturate the solution at the final temp
  3. Add the 2 values together to calculate the mass of the precipitate
22
Q

What is the equation for percentage yield?

A

percentage yield = [actual yield/predicted yield] x 100

23
Q

Name 3 reasons why the mass of a product can differ from the predicted mass?

A
  • Incomplete/ reversible reaction
  • Some of the product may be lost when it is separated from the reaction mixture
  • Some of reactants may reacts in ways different to the expected reaction

Chemistry (15 decks)

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