Answer:
(a) Dissolving sugar in water ⇒ physical change
(b) Crushing rock salt ⇒ physical change
(c) Burning sulfur ⇒ chemical change
(d) Digesting a chili dog ⇒ chemical change
Explanation:
<em>Physical changes</em> are those in which the substance does not alter its composition. They only involve changes of states of matter and the chemical substance is stil the same after the change occurs. By other hand, <em>chemical changes</em> are those in which new subtances are formed. So, the subtance is not the same after the change.
(a) Dissolving sugar in water ⇒ <em>physical change</em>; because we obtain a solution of sugar in water (sugar is stil sugar).
(b) Crushing rock salt ⇒ <em>physical change</em>; because we obtain crushed salt, but the chemical composition of the salt is not altered.
(c) Burning sulfur ⇒ <em>chemical change</em>; because sulfur is oxidized (chemical reaction) and new compounds are formed, for example sulfur dioxide.
(d) Digesting a chili dog ⇒ <em>chemical change</em>; because the digestion process is produced by the action of hydrocloric acid, and new compounds are formed.
Answer: A. 2 Sodium hydroxide molecules is 2NaOH and sulfuric acid is H2SO4
Answer: Percent yield represents the ratio between what is experimentally obtained and what is theoretically calculated, multiplied by 100%.
% yield
=
actual yield
theoretical yield
⋅
100
%
So, let's say you want to do an experiment in the lab. You want to measure how much water is produced when 12.0 g of glucose (
C
6
H
12
O
6
) is burned with enough oxygen.
C
6
H
12
O
6
+
6
O
2
→
6
C
O
2
+
6
H
2
O
Since you have a
1
:
6
mole ratio between glucose and water, you can determine how much water you would get by
12.0
g glucose
⋅
1 mole glucose
180.0 g
⋅
6 moles of water
1 mole glucose
⋅
18.0 g
1 mole water
=
7.20
g
This represents your theoretical yield. If the percent yield is 100%, the actual yield will be equal to the theoretical yield. However, after you do the experiment you discover that only 6.50 g of water were produced.
Since less than what was calculated was actually produced, it means that the reaction's percent yield must be smaller than 100%. This is confirmed by
% yield
=
6.50 g
7.20 g
⋅
100
%
=
90.3
%
You can backtrack from here and find out how much glucose reacted
65.0 g of water
⋅
1 mole
18.0 g
⋅
1 mole glucose
6 moles water
⋅
180.0 g
1 mole glucose
=
10.8
g
So not all the glucose reacted, which means that oxygen was not sufficient for the reaction - it acted as a limiting reagent.
Explanation:
It's a single- replacement reaction so Mg+ 2HCl ➡️ H2+ MgCl2
