The chalk particles embed themselves into the small pores on the surface.
Although a chalkboard seems smooth to the touch, it is quite rough at the microscopic level, with <em>pores</em> that reach below the surface.
When you drag chalk across the board, friction causes small particles of chalk to rub off onto the surface.
If you leave the markings for a long time, some of the chalk particles will work their way into the pores.
A brush will remove the surface particles, but <em>it will not be able to get at the particles in the pores</em>.
Answer:
2.04 x 10²⁴ molecules
Explanation:
Given parameters:
Mass of Be(OH)₂ = 145.5g
To calculate the number of molecules in this mass of Be(OH)₂ we follow the following steps:
>> Calculate the number of moles first using the formula below:
Number of moles = mass/molarmass
Since we have been given the mass, let us derive the molar mass of Be(OH)₂
Atomic mass of Be = 9g
O = 16g
H = 1g
Molar Mass = 9 + 2(16 + 1)
= 9 + 34
= 43g/mol
Number of moles = 145.5/43 = 3.38mol
>>> We know that a mole is the amount of substance that contains Avogadro’s number of particles. The particles can be atoms, molecules, particles etc. Therefore we use the expression below to determine the number of molecules in 3.38mol of Be(OH)₂:
Number of
molecules= number of moles x 6.02 x 10²³
Number of molecules= 3.38 x 6.02 x 10²³
= 20.37 x 10²³ molecules
= 2.04 x 10²⁴ molecules
Answer:
The new pressure of the pump is 26.05 atm or 2639.4 kPa
Explanation:
Step 1: Data given
Volume of the bicycle tire pump = 252 mL = 0.252 L
Pressure of air = 995 kPa = 9.81989 atm
The volume of the pump is reduced to 95.0 mL = 0.095 L
Step 2: Calculate the new pressure
V1*P1 = V2*P2
⇒with V1 = the initial volume of the bicycle tire pump = 0.252 L
⇒with P1 = the initial pressure of the pump = 9.81989 atm = 995 kPa
⇒with V2 = the reduced volume of the pump = 0.095 L
⇒with P2 = the new pressure = TO BE DETERMINED
0.252 L * 9.81989 atm = 0.095 L * P2
P2 = 26.05 atm
The new pressure is 26.05 atm
OR
0.252 L * 995 = 0.095 L * P2
P2 = 2639.4 kPa
The new pressure of the pump is 26.05 atm or 2639.4 kPa
Answer:
Explanation:
The density formula is mass over volume.
Rearrange the formula for the mass, m. Multiply both sides of the formula by v.
Mass can be found by multiplying the density and volume. The density is 0.65 grams per milliliter and the volume is 45.0 cubic centimeters.
- A cubic centimeter is equal to a milliliter.
- Therefore, 45 cubic centimeters also equals 45 milliliters.
Substitute the values into the formula.
Multiply. Note the milliliters, or mL will cancel out.
The mass of the wood is 29.25 grams.
