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secondary 4 | A Maths
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Why is the ans for this qn b?
If the substances in b reacts, we get magnesium nitrate which is SOLUBLE in water and hence can get Oh- ions… ph would COMFIRM be more than 7.However, qn says ph is remains constant at 7 and doesnt go beyond there.Hence, My thinking is that B is wrong and that the ans is unreliable. Anyone can help clarify? Ty.
Date Posted: 2 years ago
Views: 261
B is correct. Note that you are adding MgO, which is insoluble in water... so where do the OH- (hydroxide ions) come from? For the O-levels, you generally assume salts formed have a pH of 7... as in the case of magnesium nitrate.
Author of several O-level Science guide books (my profile pic). My forte is tutoring O-level sciences (Chemistry, Physics, Biology). Telegram Messenger: @ChillXsg Note that only my tuition students have the privilege to direct message questions, to clarify.
Author of several O-level Science guide books (my profile pic). My forte is tutoring O-level sciences (Chemistry, Physics, Biology). Telegram Messenger: @ChillXsg Note that only my tuition students have the privilege to direct message questions, to clarify.
Omg ty. I get it alr so the salt formed is always neutral hence it would obviously not hv any oh- ions to dissolve in water. We should focus on mgo instead since it is the one added.
Indeed... need to memorise solubility of common salts, carbonates and bases for
1. State symbols
2. To better understand Qualitative analysis
3. Preparation of salts
4. Ionic equations
1. State symbols
2. To better understand Qualitative analysis
3. Preparation of salts
4. Ionic equations
Anothrr qn sry. Why we cannot say ans is A tho? Didnt u said all salts formed are neutral?
Yes... salts are generally pH 7... but substance being added is aqueous ammonia, a weak alkali.. so when aqueous ammonia is in excess... the final pH would be...?
Below 7.
Sir, to correct ur first statement, mgo should be soluble in water as group 1 oxides are super soluble.
Group I oxides and salts, yes... are very soluble... but Mg is a Group II metal...
Aqueous ammonia is a weak alkali... so the final pH would be between 8 and 10.... pH below 7 is acidic...
Aqueous ammonia is a weak alkali... so the final pH would be between 8 and 10.... pH below 7 is acidic...
Ahhhh i see. Final qn:
If i change magnesium oxide and potassium oxide to calcium oxide and lead 2 Oxide respectively, as in change the qn.
How would u do this qn?
Both oxides are INSOLUBLE
If i change magnesium oxide and potassium oxide to calcium oxide and lead 2 Oxide respectively, as in change the qn.
How would u do this qn?
Both oxides are INSOLUBLE
CaO is slightly soluble and dissolves to form Calcium hydroxide. Saturated calcium hydroxide is used as limewater (test for CO2 gas) and typically has a pH from 11 to 13 (strong alkali). PbO is an insoluble yellow powder.
Your foundation facts on acids and bases needs to be reviewed and properly memorised...
Your foundation facts on acids and bases needs to be reviewed and properly memorised...
My teacher told me to assume partially soluble to be insoluble tho.
No comment to that... haha
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