Chap 1: Acids and Hydrogen Flashcards
1
Q
leaves turn yellow
why:
color: ? → ?
properties:
A
leaves turn yellow
why: chlorophyll is broken down and xanthophyll (yellow) is formed
color: green → yellow
properties: chemical (new substance is formed)
2
Q
physical change
A
- size and shape changes
- states of matter changes
states of matter example: liquid to gas, gas to solid, etc…
3
Q
chemical change
A
- corrosion, combustion, burning, exploding, rusting, rotting
- colour change
- respiration and digestion
- new subtance is formed
4
Q
main component of candle
A
carbon and hydrogen
5
Q
product for combustion of candle
A
carbon dioxide and water vapour
6
Q
what is used to test for water vapour
A
cobalt chloride paper
7
Q
what is used to test for carbon dioxide
A
limewater, if there is the presence of CO², limewater turns milky
8
Q
proof that new matter are formed
A
-
colour change:
i. fallen leaf turns yellow as chlorophyll decomposes
ii. silverware darkens after being exposed to the air for a long time -
gases and precipitate produced:
i. electrolysis of water
ii. carbon dioxide dissolves in limewater -
energy change: (temperature change)
i. energy conversion during the burning of a candle, chemical energy → heat and light energy
precipitate: a substance that will settle and becomes a solid at the bottom (usually like milky)
9
Q
importance of studying chemical changes
A
- ozone: strong oxidizing power that kills bacteria → used to treat harmful micro-organisms in tap water
- copper sulphate: changes color when in contact with water → test the presence of water in alcohol
10
Q
acids
A
- includes H+
- sour
- corrosive
11
Q
example of acid
A
- lemon → citric acid
- vinegar → acetic acid
- carbonated drinks → carbonic acid
12
Q
common acids
A
- hydrochloric acid (HCl)
- sulphuric acid (H2 SO4)
- nitric acid (HNO3)
13
Q
ionisation
A
when acid dissolves in water, water molecules reduce the force of attraction between hydrogen and acid radicals, hence becoming free-moving ions
14
Q
acid radical
A
the negative ion produced by the ionisation of acid
15
Q
ionic equation of hydrochloric acid
A
H+ Cl-
16
Q
ionic equation of sulphuric acid
A
2H+ SO4^2-
17
Q
ionic equation of nitric acid
A
H+ NO3^-
18
Q
litmus paper and phenolphthalein is called? why?
A
acid-base indicators shows different colours in solutions of different acidity
19
Q
litmus solution changes
A
normal/distilled water: purple
acid: turns red
alkaline/base: turns blue
20
Q
phenolphthalein changes
A
normal/distilled water: colourless
acid: colourless
alkaline/base: turns red/pink
21
Q
methyl orange
A
normal/distilled water: orange
acid: turns red
alkaline/base: turns yellow
22
Q
chemical equation for
* sulphuric acid + sodium hydroxide:
* hydrochloric acid + sodium hydroxide:
A
- sulphuric acid + sodium hydroxide:
H2SO4 + NaOH→ Na2 SO4 + H2O
H2SO4 + 2NaOH→ Na2 SO4 + 2H2O - hydrochloric acid + sodium hydroxide:
HCl + NaOH → NaCl + H2O
23
Q
neutralization
A
- acid (anion) + base (cation) → salt + water
- example:
1) H+Cl- + Na+ OH- → NaCl + H2O
2) H2+SO4- + 2K+OH- → K2SO4 + 2H2O
24
Q
main compound of rusted iron nail
A
iron (III) oxide
25
acids react with metal oxides to form salt and water
* CuO + 2HCl → CuCl2 + H2O
* Fe2O3 + 6HCl → 2FeCl3 + 3H2O
26
when rusted iron nail is in HCl, what is seen
bubbles are formed on the surface (hydrogen)
27
no gas was supposed to produce as a rusted iron nail is in HCl, what happened
* HCl continued to react with metal ion to form gas
* 2HCl + Fe → FeCl2 + H2↑
28
salt
a compound that is made of metal ion or ammonium ion or an acid radical
29
acid + ____ → new acid + new ____
salt
30
main component of eggshells
calcium carbonate
31
calcium carbonate is
a salt (metal carbonate, metal ion)
32
when eggshells are put in HCl, what is seen?
gas bubbles are released (CO2)
33
chemical equation of eggshells + HCl
* 2HCl + CaCO3 → CaCl2 + H2CO3
* 2HCl + CaCO3 → CaCl2 + H2O + CO2 (decomposed)
* acid + metal carbonate → salt + water + carbon dioxide
## Footnote
decomposed: cause break down into component elements
34
if a lighted splint is near a tube of carbon dioxide, what happens
lighted splint will extinguish
35
hydrochloric acid properties
* pungent smell and colourless liquid
* HCl acid is the aqueous solution of HCl gas
=HCl (gas) + H2O → HCl (acid)
* concentrated HCl: highly volatile, when opened mist can be seen
=HCl (gas) + H2O (water vapour in air) → HCl (mist)
## Footnote
pungent: sharp smell
volatile: easily evaporated at normal temperatures
36
uses of hydrochloric acid
* remove rust
* manufacture drugs
* gastric juice in stomach, to aid digestion
37
Silver nitrate + hydrochloric acid (+ a bit of nitric acid) = silver chloride
* HCl + AgNO3 → AgCl↓ + HNO3
* silver chloride is a white precipitate (insoluble)
38
what is used to test for the presence of chloride ion
silver nitrate and nitric acid
39
why can silver nitrate and nitric acid be used to test for the presence of chloride ion
* silver nitrate: forms visible white precipitate of silver chloride
* nitric acid: to remove any carbonate ions that might be present
40
sulphuric acid properties
* all concentrated ↓
* hygroscopic: absorbs water vapour from the air
* strong dehydration property: removes hydrogen & oxygen atom (water) out of a substance
* strongly corrosive
41
uses of sulphuric acid
* drying agent: dries oxygen & hydrogen & carbon dioxide
* used in making fertilizers, insecticides, gunpowder, dyes
* "mother of chemical industry": used in metal smelting and petroleum refinery
* concentrated: dehydrates sucrose into carbon, white → black
42
why acid into water, x water into acid
* acids need to be slowly added into water and get stirred so any heat produced is dispersed properly
* water into acid might boil and splash out → explosion
43
barium chloride + sulphuric acid (+ a bit of nitric acid) → barium sulphate
* H2SO4 + BaCl2 → BaSO4↓ + 2HCl
*barium sulphate is a white precipitate (insoluble)
44
what is used to test for the presence of sulphate radical
barium chloride and nitric acid
45
nitric acid properties
* colourless & volatile & irritating smell
* concentrated HNO3 appears yellow as it contains brownish nitrogen dioxide (the product of decomposition of HNO3)
* reacts with almost all metals (x gold & platinum)
* strong oxidizing power: hydrogen xproduced during reaction between metals & HNO3
46
nitric acid + metal → salt + hydrogen + nitrogen oxide/dioxide
* 3Cu + 8HNO3 **(dilute)** → 3Cu (NO3)2 + 2**NO**↑ + 4H2O
* Cu + 4HNO3 **(conc.)** → Cu (NO3)2 + 2**NO2** ↑ + 2H2O
47
aqua regia
* concentrated (nitric + hydrochloric acid) in volume of 1:3
* even stronger oxidizing power → dissolves metals: gold and platinum
48
uses of nitric acid
* used in making gunpowder, fertilizers, dyes
49
chemical properties of hydrogen
* colourless, tasteless, odourless
* difficult to dissolve in water, use water displacement method
* density: 0.09g/L, lightest gas
* at -253°C, H→colourless liquid
* at -259°C, H→snow-like solid
50
color of pure hydrogen
pale blue
51
chemical equation of burning of hydrogen
2H2+O2 = 2H2O
52
hydrogen + oxygen → oxy-hydrogen
* produce water and heat
* burns up to 3000°C
* used to weld or cut metals
53
flammable limits or explosive limits
* when air mixes with hydrogen that occupies 4%-74.2% of total volume, ignition will cause explosion
* purity of hydrogen needs to be checked before ignition
## Footnote
purity: release
54
how to test for hydrogen
get a lighted splint close to a test tube with hydrogen, it will produce a 'pop' sound in the presence of pure hydrogen
55
hydrogen is a drying agent/ this phenomenon is called reduction
explain:
black copper (II) oxide → ?
white anhydrous copper sulphate → ?
* explain: hydrogen is able to take place of oxygen in a metal oxide and reduce the oxide to a metal
* H2 + CuO → Cu + H2O
* black copper (II) oxide → turns brownish red copper
* white anhydrous copper sulphate → turns blue in the presence of water vapour produced
56
uses of hydrogen
* liquid hydrogen can be used as high-energy fuel
* used industrially to smelt metals
* turns liquid oil to solid fat (hardened oil), hence the production of margarine from liquid vegetable oils
* combines with nitrogen to form ammonia (NH3)
57
laboratory preparation of H
* Active metals: magnesium/zinc
* dilute acids: hydrochloric acid/ sulphuric acid
* chemical equation 1: Zn + H2SO4 → ZnSO4 + H2 ↑
* chemical equation 2: Zn + 2HCl → ZnCl2 + H2 ↑
* observation: bubbles are produced (hydrogen)
* method: downward displacement of air/ displacement of water (H is less dense than air/insoluble)
58
when laboratory preparation of H, why should the thistle funnel be immersed in acid?
to prevent gases leaked from the mouth of thistle funnel
59
industrial preparation of H
* reacting steam with hot iron filings or coal/ methane
* utilization of solar energy and water
## Footnote
utilization: make use
