Quantitative Chemistry Flashcards
(32 cards)
What is the law of conservation of mass
No atoms are lost or made during a chemical reaction so the mass of the products equal the mass of the reactants
Where are the products and reactants
Reactants left products right
92g of sodium reacts with 32g of oxygen, calculate the mass of sodium oxide produced
92 + 32 = 124g because the mass of the product is equal to the mass of the reactants and no atoms can be lost or made in a chemical reaction
How do you work out uncertainty from sets of repeated measurements
Range of values
———————-
2
How to workout range
Maximum value - minimum value
What do group 1 metals, group 2 metals, group 6 non metals and group 7 non metals form?
- group one metals form +1 ions
- group two metals form +2 ions
- group six non metals form -2 ions
- group seven non metals form -1 ions
How to work out uncertainty using a scale such as a ruler
The uncertainty in the measurement is half of the smallest division
It would be expressed as
6.4 (biggest measurement on shape measured) -+ (minus on bottom) 0.05 (half of the smallest division)
What is the uncertainty using a digital device
The smallest digit on the device would be the uncertainty
The uncertainty would be the weight of whatever u were weighing +- the smallest digit on the scale
What are the two types of error
- random error
- systematic error
What is the error
The difference between the measured value and the true value
What is random error
An error caused by factors that vary between readings (eg reaction time)
How to calculate number of moles in elements
Number of moles = Mass (g)
——————————
Relative atomic mass Ar
How to calculate number of moles in compounds
Number of moles = Mass (g)
——————————
Relative formula mass Mr
You are given 120g of calcium, how many moles have you been given? Ar for calcium = 40
120
—— = 3 moles
40
What does abundance mean
How common an isotope is
Key facts about relative formula mass
- no units
- never involves big numbers such as 2CH
What is relative formula mass
The relative atomic masses added together
You are given a sample of calcium carbonate (CACO3) with a mass of 300g. Calculate the number of moles of calcium carbonate in the sample.
Ar Ca= 40 Ar C= 12 ArO= 16
40 + 12 + (16 x 3) = relative formula mass
= 100
300
——- = 3 moles
100
How to calculate mass (in terms of moles)
Mass (g) = number of moles x relative formula mass Mr
What does it mean if there is no big number
It’s a one (like 1 MG)
What do you have to have in order to calculate masses or products (amounts of substances in reactions
Balanced formula equations
What are molecules in an equation
The big number
What is the formula mass
The masses of each element x by the number of molecules etc
eg. 2H(small 2)O 1 H x 4 = 4 16 O x 2 = 32 32+4=36
Calculate the mass of magnesium chloride thay could be produced from 72g of magnesium. Assume that the chlorine is unlimited. Ar Mg = 24. Ar CI = 35.5
Mg + CI(small 2) ———-> MgCI(small 2)
No of moles= 72
—— = 3 moles (Mg) —> 3 moles (MgCI)
24
Mass = 3 x 95 (relative formula mass of MgCI) = 285g
