The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

GCSE chem question: what are bases?

Im really confused about what bases are, as I know its an alakli that has been dissolved in water, but how do I identify one? Like my friend told me that they are usually hydroxides, but on yt, it says that they are metal oxides, and that ALKALIS's are metal hydroxides, so im VERy confused.

I have a test on it tomorrow, so I would appreciate any help! Thank you xx
Reply 1
Avatar for LucyJl
LucyJl
10
Original post by vix.xvi
Im really confused about what bases are, as I know its an alakli that has been dissolved in water, but how do I identify one? Like my friend told me that they are usually hydroxides, but on yt, it says that they are metal oxides, and that ALKALIS's are metal hydroxides, so im VERy confused.

I have a test on it tomorrow, so I would appreciate any help! Thank you xx

I do Chem Alevel and can confirm that what the person said above is correct - Hydroxides are usually alkali yes as they will donate OH- ions (you don't need to know this at GCSE) essentially anything with an OH will be an alkali eg Mg(OH)2
Original post by LucyJl
I do Chem Alevel and can confirm that what the person said above is correct - Hydroxides are usually alkali yes as they will donate OH- ions (you don't need to know this at GCSE) essentially anything with an OH will be an alkali eg Mg(OH)2

Ty!!
Are metal oxides bases too? or ary they alkalis xx
Original post by Zoqua
I'm not doing Chemistry A level, and have never particularly loved the subject, but I got a 9 at GCSE (mainly by just memorizing freesciencelessons), so I can tell you what to say for your exam:
Say this if asked:
-Bases are chemicals that can neutralize acids to form a salt and water (that's an easy 2 marker).
-If asked, an Alkali is just a base that is soluble in water.

I'm pretty sure this is everything you need to know for GCSE for the simple definitions. Here is freesciencelessons' video on it (basically what I said but in more detail with examples): https://www.youtube.com/watch?v=wmhOttroIrw

Good luck with your exam :smile:

woah tysmmm!
Original post by vix.xvi
Im really confused about what bases are, as I know its an alakli that has been dissolved in water, but how do I identify one? Like my friend told me that they are usually hydroxides, but on yt, it says that they are metal oxides, and that ALKALIS's are metal hydroxides, so im VERy confused.

I have a test on it tomorrow, so I would appreciate any help! Thank you xx

Think of a venn diagram. The 'base' is a big circle, and 'alkali' is a small circle within the big circle.

A base is basically a molecule that accepts an H+ ion (proton). It can be difficult to identify a base, since many molecules are able to act as either a base or an acid.
Strong bases include: NaOH, KOH, etc... pretty much any metal with a hydroxide group. Metal oxides are also bases (e.g. MgO, CaO...)
There are also bases that are carbonates, e.g. CaCO3 + 2HCl -> H2O + CO2 + CaCl2

A good way to remember how to write the reactions:

AAWS: acid + alkali -> water + salt
BAWS: acid + base -> water + salt
CAWCS: carbonate + acid -> water + carbon dioxide + salt
MASH: metal hydride + acid -> salt + hydrogen

I don't know if you need to learn it, but there are also many weak bases that are less easy to spot e.g. NH3 (it has a lone pair thus can accept an H+). Any molecule that has a lone pair can potentially act as a base (if you don't know, lone pair = 2 outer electrons that are not involved in a bond)
Reply 5
Avatar for LucyJl
LucyJl
10
Original post by vix.xvi
Ty!!
Are metal oxides bases too? or ary they alkalis xx


Metal oxides are bases because they'll react with an acid to form salt + water - essentially anything that makes water will be a base / alkaline and if it forms hydrogen it will be acidic (I think) - also don't worry about this too much as long as you know the basic equations:

metal + acid = salt + hydrogen
metal carbonate + acid = salt + CO2 + water
acid + base = salt + water
metal oxide + acid = salt + water

also I rate the CGP revision guides I found them really helpful and don't forget to keep doing practice papers - you're lucky you've got more than I did haha I was the first year doing 9-1

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you