3-Quantitative Chemistry Flashcards

1
Q

What is relative formula mass?

A

Mr of a compound is the sum of the relative formula masses of the atoms in the numbers shown in the formula.

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2
Q

What is true about Mr in a balanced chemical equation?

A

Mr of products and reactants are equal in a balanced symbol equation.

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3
Q

what is the law of conservation of mass?

A

No atoms are lost or made during a chemical reaction, mass of products=mass of reactants

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4
Q

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

A

Ar X number of atoms of that element / Mr of the compound X 100

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5
Q

What is the mole?

A

How chemical amounts are measured

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6
Q

What is mass of 1 mol of a substance equal to?

A

Mass of 1 mol of a substance in grams = its relavtive formula mass

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7
Q

What is avagadro’s constant?

A

the number of atoms, molecules or ions, in a mol of any given substance

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8
Q

What is the value for avagadro’s constant?

A

6.02 X 10^23

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9
Q

How do you calculate number of moles?

A

number of moles = mass in g / Relative atomic mass (Mr)

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10
Q

Why may mass in a reaction appear to change?

A

A gas is involved and its mass has not been taken into account.

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11
Q

How can balancing numbers in a symbol equation be calculated from masses of reactants and products?

A

Converting masses in grams to amounts in moles and converting the numbers of moles to simple whole number ratios.

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12
Q

When do reactions stop?

A

When limiting reactant is used up

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13
Q

What is a limiting reactant?

A

The reactant that is completely used up - because it limits amount of products.

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14
Q

What is the volume of one mole of any gas at room temp and 1 atmospheric pressure?

A

24 dm^3

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15
Q

What can concentration of a solution be measured in?

A

Mass per given volume of solution, e.g g/dm^3

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16
Q

What is the calculation for concentration in mol/dm^3?

A

conc = no of moles/volume

17
Q

*How do you convert mol/dm^3 to g/dm^3?

A

Mass = moles X Mr

18
Q

Why is it not always possible to obtain a calculated amount of a product?

A

*reaction may not go to completion because its reversible
*some product may be lost when separated from reaction mixture
*some reactants may react differently than expected

19
Q

What is the yield?

A

Amount of product obtained.

20
Q

What is the formula for percentage yield?

A

percentage yield = mass of actual products/maximum theoretical mass X 100

21
Q

Why can yield never be 100%

A

Some of the product or reactant always gets lost along the way.

22
Q

What is atom economy?

A

Percentage of reactants forming useful products

23
Q

Why is higher atom economy desired?

A

Less waste as more useful products, better economically?

24
Q

What is the atom economy equation?

A

Mr of desired products/ Mr of all reactants

25
Q

What is uncertainty?

A

The amount of error a measurement may have

26
Q

How can uncertainty be calculated?

A

range/2

27
Q

What could be causes of error?

A
  • random error
  • errors in measuring equipment