Answer:
Pb₂O₄
Explanation:
The given species are:
Pb⁴⁺ O²⁻
Now, to solve this problem, we use the combining powers which corresponds to the number of electrons usually lost or gained or shared by atoms during the course of a chemical combination.
Pb⁴⁺ O²⁻
Combining power 4 2
Exchange of valencies 2 4
Now the molecular formula is Pb₂O₄
Answer: Option (c) is the correct answer.
Explanation:
Plants used to prepare food in the presence of sunlight. Therefore, plants uses solar energy to make food.
Due to solar energy various chemical reactions take place in the food.
Thus, we can conclude that chemical energy is stored in our food and this chemical energy start out as light energy from the sun.
Answer:
1) 1.202 L
, 2) 1.291 dg
, 3) 204.877 and 4) 1.04x
Explanation:
You need to review about conversion factors and how to use them in the correct order. You can cancel the units and get the ones that you need if you use the appropriate conversion factors, remember is a number that you can use to multiply or divide.
For your exercise:
1) The conversion factor is: 1 L = 1000 mL
You will need to divide by 1000 mL to obtain liters L
1202.57120 mL x 
= 1.202 L
2) The conversion factor is: 1 g = 10 dg
0.1290743 g x 
= 1.291 dg
For the next exercises, you need to follow some rules:
1. All numbers that are different from Zero (non-zero digits) are significant figures.
2.The Zeros between non-zeros digits (Imbedded zeros) always are significant, 2007.
3. If you want to be specific and want some zeros to be significant you need to add a decimal point. For example 500. or 500.0
4. Leading zeros (to the left) are not significant.
5. Trailing zeros (zeros to the right) in a whole number without decimal point are not significant.
3) 843.062 - 638.1848 = 204.8772
Now if we round to 6 significant figures we get 204.877
4)123.0 x 8.43 = 1036.89
Now we round to 3 significant figures because 8.43 has the least significant figures.
1.04x
This question is testing to see how well you understand the "half-life" of radioactive elements, and how well you can manipulate and dance around them. This is not an easy question.
The idea is that the "half-life" is a certain amount of time. It's the time it takes for 'half' of the atoms in any sample of that particular unstable element to 'decay' ... their nuclei die, fall apart, and turn into nuclei of other elements.
Look over the table. There are 4,500 atoms of this radioactive substance when the time is 12,000 seconds, and there are 2,250 atoms of it left when the time is ' y ' seconds. Gosh ... 2,250 is exactly half of 4,500 ! So the length of time from 12,000 seconds until ' y ' is the half life of this substance ! But how can we find the length of the half-life ? ? ?
Maybe we can figure it out from other information in the table !
Here's what I found:
Do you see the time when there were 3,600 atoms of it ?
That's 20,000 seconds.
... After one half-life, there were 1,800 atoms left.
... After another half-life, there were 900 atoms left.
... After another half-life, there were 450 atoms left.
==> 450 is in the table ! That's at 95,000 seconds.
So the length of time from 20,000 seconds until 95,000 seconds
is three half-lifes.
The length of time is (95,000 - 20,000) = 75,000 sec
3 half lifes = 75,000 sec
Divide each side by 3 : 1 half life = 25,000 seconds
There it is ! THAT's the number we need. We can answer the question now.
==> 2,250 atoms is half of 4,500 atoms.
==> ' y ' is one half-life later than 12,000 seconds
==> ' y ' = 12,000 + 25,000
y = 37,000 seconds .
Check:
Look how nicely 37,000sec fits in between 20,000 and 60,000 in the table.
As I said earlier, this is not the simplest half-life problem I've seen.
You really have to know what you're doing on this one. You can't
bluff through it.
1) is called 3-methyl hexane because we choose the longest possible continuous chain which has 6 carbons and start numbering from the side that gives the branch lowest possible number.
2) is called 2-methyl-2-butene because we have to give the double bond lowest possible number but in this case double bond in position 2 from both sides so we start from the side gives the branch number 2 not 3
3) is called 7-Ethyl-4-decyne because we have to start from the side that gives the triple bond lowest possible number which is 4 and the branch will be at position 7 (note that the name of 10 carbon is incorrectly written in the choices is called decane (as alkane) or decyne when contains triple bond)
4) is called 2,3-Dimethyl pentane because it is 5 carbons (pentane) and we have two branches of the same alkyl (dimethyl) in positions 2 and 3
5) is called 1-Butanol because it contains 4 carbons and has one OH as functional group which take the suffix -ol in position 1 so we said the name as 1-butanol (remember to give the functional group lowest possible number)
6) is called propyl butyl ether because the longest chain is 4 carbons which called butyl and the smallest chain is propyl, it also has another name 1-Propoxy butane <span />
