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0.9 Quantitative aspects of chemical change  (Page 4/10)

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Calculate the number of atoms there are in a sample of aluminium that weighs 80 , 94 g .

  1. n = m M = 80 , 94 26 , 98 = 3 moles

  2. Number of atoms in 3 mol aluminium = 3 × 6 , 022 × 10 23

    There are 18 , 069 × 10 23 aluminium atoms in a sample of 80 , 94 g .

Some simple calculations

  1. Calculate the number of moles in each of the following samples:
    1. 5 , 6 g of calcium
    2. 0 , 02 g of manganese
    3. 40 g of aluminium
  2. A lead sinker has a mass of 5 g .
    1. Calculate the number of moles of lead the sinker contains.
    2. How many lead atoms are in the sinker?
  3. Calculate the mass of each of the following samples:
    1. 2,5 mol magnesium
    2. 12 mol lithium
    3. 4 , 5 × 10 25 atoms of silicon

Molecules and compounds

So far, we have only discussed moles, mass and molar mass in relation to elements . But what happens if we are dealing with a molecule or some other chemical compound? Do the same concepts and rules apply? The answer is 'yes'. However, you need to remember that all your calculations will apply to the whole molecule . So, when you calculate the molar mass of a molecule, you will need to add the molar mass of each atom in that compound. Also, the number of moles will also apply to the whole molecule. For example, if you have one mole of nitric acid ( HNO 3 ), it means you have 6 , 022 × 10 23 molecules of nitric acid in the sample. This also means that there are 6 , 022 × 10 23 atoms of hydrogen, 6 , 022 × 10 23 atoms of nitrogen and ( 3 × 6 , 022 × 10 23 ) atoms of oxygen in the sample.

In a balanced chemical equation, the number that is written in front of the element or compound, shows the mole ratio in which the reactants combine to form a product. If there are no numbers in front of the element symbol, this means the number is '1'.

e.g. N 2 + 3 H 2 → 2 N H 3

In this reaction, 1 mole of nitrogen reacts with 3 moles of hydrogen to produce 2 moles of ammonia.

Calculate the molar mass of H 2 SO 4 .

  1. Hydrogen = 1,008 g · mol - 1 ; Sulphur = = 32,07 g · mol - 1 ; Oxygen = 16 g · mol - 1

  2. M ( H 2 S O 4 ) = ( 2 × 1 , 008 ) + ( 32 , 07 ) + ( 4 × 16 ) = 98 , 09 g · mol - 1

Calculate the number of moles there are in 1 kg of MgCl 2 .

  1. n = m M
    1. Convert mass into grams
      m = 1 kg × 1 000 = 1 000 g
    2. Calculate the molar mass of MgCl 2 .
      M ( MgCl 2 ) = 24 , 31 + ( 2 × 35 , 45 ) = 95 , 21 g · mol - 1
  3. n = 1000 95 , 21 = 10 , 5 mol

    There are 10 , 5 moles of magnesium chloride in a 1 kg sample.

Barium chloride and sulphuric acid react according to the following equation to produce barium sulphate and hydrochloric acid.

BaCl 2 + H 2 SO 4 → BaSO 4 + 2 HCl

If you have 2 g of BaCl 2 ...

  1. What quantity (in g) of H 2 SO 4 will you need for the reaction so that all the barium chloride is used up?
  2. What mass of HCl is produced during the reaction?
  1. n = m M = 2 208 , 24 = 0 , 0096 mol

  2. According to the balanced equation, 1 mole of BaCl 2 will react with 1 mole of H 2 SO 4 . Therefore, if 0 , 0096 mol of BaCl 2 react, then there must be the same number of moles of H 2 SO 4 that react because their mole ratio is 1:1.

  3. m = n × M = 0 , 0096 × 98 , 086 = 0 , 94 g

    (answer to 1)

  4. According to the balanced equation, 2 moles of HCl are produced for every 1 mole of the two reactants. Therefore the number of moles of HCl produced is ( 2 × 0 , 0096 ), which equals 0 , 0096 moles .

  5. m = n × M = 0 , 0192 × 35 , 73 = 0 , 69 g

    (answer to 2)

Questions & Answers

What is inflation
Bright Reply
a general and ongoing rise in the level of prices in an economy
AI-Robot
What are the factors that affect demand for a commodity
Florence Reply
price
Kenu
differentiate between demand and supply giving examples
Lambiv Reply
differentiated between demand and supply using examples
Lambiv
what is labour ?
Lambiv
how will I do?
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information
Eliyee
devaluation
Eliyee
t
WARKISA
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Lambiv
multiple choice question
Aster Reply
appreciation
Eliyee
explain perfect market
Lindiwe Reply
In economics, a perfect market refers to a theoretical construct where all participants have perfect information, goods are homogenous, there are no barriers to entry or exit, and prices are determined solely by supply and demand. It's an idealized model used for analysis,
Ezea
What is ceteris paribus?
Shukri Reply
other things being equal
AI-Robot
When MP₁ becomes negative, TP start to decline. Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 • Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of lab
Kelo
Extuples Suppose that the short-run production function of certain cut-flower firm is given by: Q=4KL-0.6K2 - 0.112 • Where is quantity of cut flower produced, I is labour input and K is fixed capital input (K-5). Determine the average product of labour (APL) and marginal product of labour (MPL)
Kelo
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Shukri
Can I ask you other question?
Shukri
what is monopoly mean?
Habtamu Reply
What is different between quantity demand and demand?
Shukri Reply
Quantity demanded refers to the specific amount of a good or service that consumers are willing and able to purchase at a give price and within a specific time period. Demand, on the other hand, is a broader concept that encompasses the entire relationship between price and quantity demanded
Ezea
ok
Shukri
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Lilia Reply
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Fiker Reply
Economic growth as an increase in the production and consumption of goods and services within an economy.but Economic development as a broader concept that encompasses not only economic growth but also social & human well being.
Shukri
production function means
Jabir
What do you think is more important to focus on when considering inequality ?
Abdisa Reply
any question about economics?
Awais Reply
sir...I just want to ask one question... Define the term contract curve? if you are free please help me to find this answer 🙏
Asui
it is a curve that we get after connecting the pareto optimal combinations of two consumers after their mutually beneficial trade offs
Awais
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Asui
In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities, where neither p
Cornelius
In economics, the contract curve refers to the set of points in an Edgeworth box diagram where both parties involved in a trade cannot be made better off without making one of them worse off. It represents the Pareto efficient allocations of goods between two individuals or entities,
Cornelius
Suppose a consumer consuming two commodities X and Y has The following utility function u=X0.4 Y0.6. If the price of the X and Y are 2 and 3 respectively and income Constraint is birr 50. A,Calculate quantities of x and y which maximize utility. B,Calculate value of Lagrange multiplier. C,Calculate quantities of X and Y consumed with a given price. D,alculate optimum level of output .
Feyisa Reply
Answer
Feyisa
c
Jabir
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Source:  OpenStax, Chemistry grade 10 [caps]. OpenStax CNX. Jun 13, 2011 Download for free at http://cnx.org/content/col11303/1.4
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