chapter 11, chemical changes

Question 1

what is matter?

Answer 1

anything that has both mass and volume, the “stuff” of the universe: books, planets, trees, people

Question 2

what is composition?

Answer 2

the types and amounts of simpler substances that make up a sample of matter

Question 3

what are properties?

Answer 3

the characteristics that give each substance a unique identity

Question 4

what are the physical properties?

Answer 4

physical properties are properties a substance shows by itself without interacting with another substance:
- color, melting point, boiling point, density

Question 5

what are chemical properties?

Answer 5

chemical properties are properties a substance shows as it interacts with, or transforms into, other substances:
-flammability, corrosiveness

Question 6

identifying chemical changes from physical changes

Answer 6

physical changes are changes in which no new substances are formed.
chemical changes can be classified into:
- reactions in which two or more substances chemically combine to form one or more new substances
- reactions in which a new substance breaks down into two or more new substances

Question 7

states of matter? and their particle formations

Answer 7

solid: fixed shape and volume. may be hard or soft, rigid or flexible. – particles are close together and organised
liquid: varying shape that conforms to the shape of the container but has a fixed volume. liquid has an upper surface. – particles are close together but disorganised
gas: has no fixed shape or volume and therefore does not have a surface. – particles are far apart and disorganised

Question 8

changes of state and temperature – physical or chemical?

Answer 8

• A change of state is a physical change. Physical form changes, composition does not.
• Changes in physical state are reversible by changing the temperature.
• A chemical change cannot simply be reversed by a
  change in temperature.

Question 9

conservation of mass

Answer 9

matter is neither created nor destroying by chemical reactions or physical changes
chemical reactions involve the rearrangement of existing atoms, therefore there is no loss or gain of atoms.
the mass of the system is the same before and after the reaction.
the number and type of atoms does not change

Question 10

different types of chemical changes?

Answer 10

combustion – a chemical reaction in which a substance is heated in the presence of oxygen
thermal decomposition – a process in which a substance breaks into two or more simpler substances upon heating
oxidation – gain of oxygen (e.g. rusting)
neutralisation – when an acid and a base react to form water and a salt

Question 11

what are the properties of an acid? and what are the different acids?

Answer 11

the hydrogen (H+) ions are responsible for the properties of an acid. they have:
- a sour taste
- they turn blue litmus paper red
- they dissolve in water to form solutions which can conduct electricity
acids:
HNO3 (aq) – nitric acid
H2SO4 (aq) – sulfuric acid
HCl (aq) – hydrochloric acid

Question 12

what are the products of an acid base reaction?

Answer 12

base + acid -> salt + water

Question 13

what are the products of an acid metal reaction?

Answer 13

metal + acid -> salt + hydrogen gas

Question 14

what are the products of an acid carbonate reaction?

Answer 14

carbonate + acid -> salt + water + carbon dioxide gas

Question 15

what are the properties of an alkali? and what are the different alkalis?

Answer 15

Alkalis are substances that produce hydroxide ions (OH-)
when it is dissolved in water. they feel soapy when touched, common household chemicals like bleach and toothpaste contain alkalis.
alkalis:
NaOH – sodium hydroxide
KOH – potassium hydroxide
Ca(OH)2 – calcium hydroxide (limewater)
NH4OH – aqueous ammonia

Question 16

how to balance Mg2+ and O2-?

Answer 16

since 1x +2charge balances out 1x 2- charge, the formula would be MgO.

Question 17

Ca2+ + NO3-1 =?

Answer 17

Ca(NO3)2

Question 18

How do you balance H2 (g) + O2 (g) ?

Answer 18

The chemical equation is balanced by adding a number in front of the chemical formula. This is the same as multiplying the formula by that number.
2H2 (g) + O2 (g) = 2H2(l) + H2O

Question 19

which part of the pH scale is acidic, neutral and alkaline

Answer 19

1- 6 acidic (1 is strongest, 6 is weakest)
7 neutral
8 - 14 alkaline (8 is weakest, 14 is strongest)

Question 20

what are the different ways we can measure pH?

Answer 20

-chemical compound called an indicator
-pH sensor attached to a data logger
-pH meter

Question 21

what are the different indicators and what colour do they change in acidic and alkaline solutions? (ni,cs)

Answer 21

litmus - red (ac), blue (al)
methyl orange - red (ac), yellow (al)
screened methyl orange - violet (ac), green (al)
phenolphthalein - colourless (ac), pink (al)

Question 22

application: pH of soils, give examples

Answer 22

it is important to control the pH of soil because it will affect the growth and development of plants
potatoes grow well at 5.5-6.5
cabbages grow well at 7.5-8.5

Question 23

controlling pH of soil

Answer 23

soil may be unsuitable for plant growth bc of:
too much fertilisers, environmental pollution such as acid rain.
to treat acidity, add:
calcium oxide (quick lime), calcium hydroxide (slaked lime)
this process is aka ‘liming’. they neutralise the acid.

Question 24

application of neutralisation?

Answer 24

Antacids
Ingredient of antacids neutralise stomach acid

Question 25

how do chemical changes occur?

Answer 25

• mixing - neutralisation
• heating - thermal decomp
• photosynthesis - photosynthesis
• exposure to light - cause colour change or fading on floors or clothes
• interacting with oxygen - copper undergoes chemical reactions with water and oxygen to make new compounds
• using an electric current - electroplating

Question 26

how do they help us in our daily lives?

Answer 26

• cooking - helps with the color, flavor and aroma (maillard reaction)
• respiration - cellular respiration
• decay
• rusting
• combustion