revision: Chemistry - Topic 3

4.4 - define acids as sources of hydrogen ions, H⁺, and alkalis as sources of hydrogen ions, OH^-

The main acids you have to remember are:

Nitric acid - HNO3

Sulphuric acid - H₂SO4

Hydrochloric acid - HCl

-All acids contain hydrogen ions (H⁺) However, not all compounds that contain hydrogen are acidic.

-Acids are only acids when in water (solution). This is due to dissociation. They split up into positive and negative charged ions. Only then is there a H⁺

-Due to this, acids have a sour taste. H⁺ also is responsible for the effect acids have on indicators.

-As hydrogen has only one proton in the nucleus, when electron is loss there is a single proton. H⁺ is a proton. 

-Not all acids are harmful, we have lactic acid in our stomach!

-The more water mixed in an acid, the more dilute it is

-

The main alkalis you have to remember are:

Ammonium hydroxide (ammonia solution) - NH₄OH

Limewater - Ca(OH)2

Sodium Hydroxide - NaOH

-Alkalis dissociate to hydrogen oxide ions. (OH^-)

-OH^- is responsible for the bitter taste and the effect alkalis have on indicators.
-All alkalis are bases but not all bases are alkalis
-Bases that dissolve in water are alkalis.

2.11 - understand the difference between hydrogen chloride gas and hydrochloric acid

-An acid is only an acid when in water, therefore hydrogen chloride gas is not an acid but hydrochloric acid is...an acid -.- like it's name.
The difference is....
HCl (g) = hydrogen chloride gas (NOT AN ACID)
HCl (aq) = hydrochloric acid (ACID ACID ACID)
hydrochloric acid is a solution of hydrogen chloride gas

2.12 -explain in terms of dissociation, why hydrogen chloride is acidic in water but not in methylbenzene

-Again, an acid is only an acid when in water!! As a solution...if it methylbenzene then it DOES NOT WORK! It's like...chickens can only be born if you hatch a chicken egg...you wouldn't just randomly get a duck -.-

This is because water is needed for dissociation to occur, it is essential for acidic behaviors to be shown....
You have HCl (g) but when you put it in water you get HCl (aq) which comes as H⁺ and Cl^- and you need that hydrogen ion (proton) for it to be acidic remember? This only happens in water...so yeah :D

Questions may say that they tested HCl in water using marble chips, magnesium or blue litmus paper...
magnesium will reaction the hydrochloric acid so you get effervescence.
blue litmus paper if damp with water will turn red to show it is acidic, however only if you dampen it with water.

4.1 - describe the use of the indicators phenolphthalein, litmus and methyl orange to distinguish between acidic and alkaline solutions

phenolphthalein is clear in acid and pink in alkali! CAPA I guess... clear acid pink alkali :D
You use this in alkali to see the change from acid to alkali because it's easy to see clear going pink (magic!) rather than pink to clear.

methyl orange is Red in acid and yellow in alkali!
You use this in acid to show change from alkali to acid because in alkali, there isn't a significant color change (and we all like to see magic color changes don't we? :D )

litmus paper - use blue for acid and red for alkali. It's the opposite of the pH color! cuz acid is already red, you gotta put it on blue litmus paper and it will become red. Alkali is purple/blue so put it on red to see it go blue! (Again, who doesn't like magic color changes?)

U.I - who doesn't know this? - Seriously if you don't you're dead tomorrow.... Universal indicators was probably the first topic you cover...in Y7 in Science...cuz what 11/12 year old wouldn't like magic color changes :D :D :D (I still do -.- don't judge me!!!!)

RAINBOW!!! Red = strong acid, keep going and it gets weaker when you get to green = neutral! and keep going to my favorite color blue = weak alkali and then you get to purple = strong alkali
It's the best cuz you can use it for everything!! Neutralization may be difficult because...to get it exactly green is hard...

4.2 understand how the pH scale, 0-14, can be used to classify solutions as strongly acidic, weakly acidic, neutral, weakly alkaline or strongly alkaline

If you have add an acid to an alkali, you can neutralize it!

4.3 - describe the use of universal indicator to measure the approximate pH value of a solution

The universal indicator colors can be used with the pH scale :D Colors match and you can look at it for numbers.
pH is the level of acidity or alkalinity.
-The colors are give due to the concentration of H⁺ or OH^- ions, which makes up an acid and alkali. When the amount of ions in the solution are equal, it is neutral.
=Higher concentration of H⁺ will make the solution acidic.
=Higher concentration of OH^- ions will make it alkaline.
The strength of an alkali or an acid is its concentration of ions, the pH of a solution is give depends on this concentration.

4.5 - predict the products of reactions between dilute hydrochloric, nitirc and sulphuric acids; and metals, metal oxides and metal carbonates (excluding the reactions between nitric, acid and metals)

Hydrochloric acid gives you chlorides.
Sulphuric acid gives you suphate
Nitric acid gives you nitrate

ACID + METAL -> SALT + HYDROGEN
Just join the names of the acid and metal...remember to change the acid names like I told you above!
ACID + BASE -> SALT + WATER
ACID + ALKALI -> SALT WATER
With the salt, a displacement occurs...the water is taken out remember :D :D :D
ACID + CARBONATE -> SALT + WATER + CARBON DIOXIDE
Same with this, but carbonate gives you carbon dioxide too!

Don't forget to balance and include state symbols when asked.

4.6 - understand the general rules for predicting the solubility of salts in water:

i) all common potassium, sodium, and ammonium salts are soluble

ii) all nitrates are soluble

iii) common chlorides are soluble, except silver chloride

iv) common sulphates are soluble, except those of barium and calcium

v) common carbonates are insoluble, except those of sodium, potassium and ammonium

-All nitrates are soluble, so are potassium, sodium and ammonium salts - all hydroxides/all sulphides, carbonates and phosphates are insoluble except potassium, sodium and ammonium.
-Chloride, bromide and iodide are soluble except for silver, mercury and lead.
All sulpates are soluble except barium lead and calcium

4.7 - describe experiments to prepare soluble Salts from acids

You can do this with 2 methods...titration or adding excess base.
Titration - Use titration to figure out what volume of acid or alkali is needed for solution to be neutralized. After that the solution can be heated and evaporated, this can then be crystallized to produce the salts.

Excess base - You can add excess base to the acid so that no more can react, stir so that no more will dissolve then filter the excess so that you get a solution. Again, evaporate the solution and crystallize to get the crystals. It doesn't work well with alkalis or solids that dissolve so sodium, potassium and ammonium will not work.

4.9 - describe experiments to carry out acid - alkali titrations
Use a volumetric propette to measure out the volumes.
You can titrate alkali into acid or acid into alkali...

You use a burette :D :D :D (I think everything end in -ette cuz their girls y'know :D :D :D) and a conical flask...
Put the indicators into the conical flask...
You use methyl orange if you are putting alkali into acid.
You use phenolphthalein if you are putting acid into alkali.
Take an average of 3 titrations...1st one if to find an approximate.
For the final one, no indicator is used as it will contaminate the salt you should have discovered the amount of volume needed for neutralization.

Evaporate by heating and then crystallize,

*Didn't explain this very well...use the revision sheet...
-FROM REVISION SHEET ->

4.9) Describing the Titration Experiments:

·      A 25cm³ volumetric pipette is used (with a pipette filler) rather than a measuring cylinder – more accurate in measuring volumes

·      The alkali can be titrated into the acid or vice versa

·      The solution in the burette is called the titrant

·      The flask stands on a white tile – colour change  is easier to see

·      Titrating alkali into acid – Phenolphthalein is used as indicator – changes from colourless to pink – the palest pink indicates neutrality – the end point

·      Titrating acid into alkali - Methyl Orange is used as indicator – gives clear & distinct colour changes: yellow à orange à red – the orange colour indicates neutrality – the end point

·      A more concentrated acid titrant will mean a smaller volume – called the titre – is required to reach neutrality

·      A rough titration is carried out first to find the approximate titre required

·      Three accurate titrations are carried out and the average titre calculated – this is the ‘equivalent volume’

·      After finding the ‘equivalent’ volumes no indicator is used for a final titration – it would contaminate the salt produced making it impure and changing its colour

·      With hydrated crystals the salt solution is heated until crystals form on the end of a glass rod–this shows that the solution is saturated / the salt is in excess and ready to crystallise

·      The saturated solution is left to cool – as it cools the water evaporates slowly– the salt cannot evaporate – forms crystals

4.8 - describe experiments to prepare insoluble salts using precipitation reactions

A precipitate is an insoluble solid formed in reactions of liquids and gases.
You mix two solutions together which are made of negative and positive ions.
When mixed you get a insoluble salt forming a precipitate.
You filter to separate the solution from the precipitate
They wash with distilled water to rid of any impurities...then then then...you dry :D :D :D

Won't work with soluble salts cuz they don't form precipitates D: D: D:

2.37 - describe tests for the cations:

Li⁺, Na⁺, K⁺, Ca²⁺ using flame tests
Metals change the colors of the flame :D
They identify which metal ions are present in which compounds :D
Li⁺ - Litium = RED/SCARLET/CRIMSON/DEEP RED (whatever BLOOD!!!!! VAMPIRE LIKE LITHIUM)
Na⁺ - Sodium = (Persistant) Orange (ORANGE SODAAAAAAAAAAA)
K⁺ - Potassium = LILAC
Ca²⁺ - Calcium = Brick red (BONES AS STRONG AS BRICK BROS :D)

NH⁴⁺ using sodium hydroxide solution and identifying the ammonia evolved
Cu²⁺, Fe²⁺, and Fe³⁺ using sodium hydroxide solution
A metal salt solution containing metal ions form precipitates :) Copper and iron have colors in solution but NaOH will confirm the presence.
Cu²⁺ - Copper (II) = BLUE <3
Fe²⁺ - Iron (II) = Green (SEAWEED <3)
Fe³⁺ - Iron (III) = Orange-brown (RUSTY - my uncle.)
NH⁴⁺  - No precipitate is given but the smell of ammonia gas is the indicator. (alkaline)

2.38 - describe tests for the anions:

Cl^-, Br^-, I^- using dilute nitric acid and silver nitrate solution
Compounds with silver are insoluble...they produce distinct precipitates...
Nitric acid is used to react and remove contaminants that may produce precipitates as well.
Cl^- - white
Br^- - cream
I^- - yellow
X Halide + Silver Nitrate -> Silver Halide + X Nitrate

SO4^2- using dilute hydrochloric acid and barium chloride solution
The product barium sulphate is insoluble...
Any sulphate mixed with barium chloride will give you a white precipitate...
So you know there is sulphate is it's white :D :D :D so racist -.-

To do this...you
Dissolve the compound you want to test in pure water.
Add dilute HCl (aq)
Add BaCl2 (aq)
If there is a white precipitate then suphate ions are confirmed!

CO3^2- using dillute hydrochloric acid and identifying the carbon dioxide involved.

Nitric acid to any carbonate will give you carbon dioxide so you just test for the gas and if limewater turns milky then CO2 is present and carbonate presence is confirmed!

2.39 - describe the test for gases:

hydrogen - A lighted splint will pop, cuz hydrogen is explosive and will react with oxygen.
oxygen - Re-lights a glowing splint
carbon dioxide - turns limewater milky
chlorine - smells like the pool or damp blue litmus paper is bleached.
ammonia - pungent smell, turns damp red litmus paper to blue.

Test for water. If you have anhydrous copper sulphate powder then with water is should turn blue. You can also test for boiling point of 100 degrees.

REMEMBER ;
TESTING GASES...
Less dense than air = upward delivery (eg. hydrogen, ammonia)
Denser = Downward (DOUBLE D :D :D) (eg, carbon dioxide, chlorine)
Insoluble in water = over water (water water water water water remember yet?)

Use a gas syringe if you need the volume (yes, the thing that looks like a HUUUUUUUUUUUGEEEE injection needle...scary...)

2.26 - describe the combustion of hydrogen
-Hydrogen is tested by using a lighted splint which will pop, (yes, it's explosive). Oxygen reacts with hydrogen to get water....
The combustion of hydrogen gives of heat and is highly exothermic (remember, EXO jump out!) so it's great for fuels...y'know those hydrogen powered cars (just don't... POP get it?)