Answer:
A pure element is a pure substance that has only one kind of atoms. If a substance is present in nature in elemental form, it means that the element is not very reactive as reactive elements exist in the form of their compounds with atoms of other elements. Element can be categorized as a metal or a non-metal based on some physical observable properties. Generally, metals are shiny lustrous solids and nonmetals are gases. Metals are good conductors of heat and electricity whereas nonmetals are not conductors.
Explanation:
Hope this helps:)
A is obviously out because it leads to a volume of 125.0 milliliters of the new solution and gives you a lower concentration than you were aiming for.
D is out because you are adding 75 milliliters of the stock solution, so your concentration would be too high. You only need 25.0 milometers of stock solution per 100 milliliters of the new solution.
C is also out because it leads to 50.0 milliliters stock solution per 100 milliliters of the new solution and hence the wrong concentration.
B is by default the correct answer. It also details the correct technique. First you add the stock solution (This you know from your calculations to be 25 milliliters.) then you add the water up to the volume you needed. (Because the calculations only tell you the total volume of water not what you need to add) You also add the water last so you can rinse the neck of the flask to make sure you also get all the stock solution residue into the stock solution.
I would add the final step of stirring, but B is the only answer that can be correct.
A physical change does not change the identity of the substance but the chemical change does.
Example
If you tear or shred a piece of paper it is still paper, but if you pour chemicals on it it will probably change to something else.
W=(m'/m)·100%
m'=37.2 g
m=48.5 g
w=(37.2/48.5)·100%=76.7%
Answer:
The answer is below
Explanation:
one gallon of gasoline produces 9.50 kg of carbon.
The total number of cars = 40 million
Distance covered by each car = 7930 miles
Consumption rate of the cars per miles traveled is 23.6 miles per gallon.
Hence the annual gasoline consumption by all the cars in the United States of America = (total number of cars × Distance covered by each car) ÷ Consumption rate of the cars per miles
annual gasoline consumption by all the cars = (40000000 × 7930 miles) ÷ 23.6 miles/gallon = `1.344067797 × 10¹⁰ gallons
1.344067797 × 10¹⁰ gallons = 
