Answer:
32 days
Explanation:
Half life is the amount of time it takes to get to half of the starting concentration / amount.
Starting amount = 250 g
Half life = 8 days
Amount left = 15.625 g
How many days ? That is, how many half lives....
After first Half life;
Amount left = 250 / 2 = 125 g
After second half life;
Amount left = 125 / 2 = 62.5 g
After third half life;
Amount left = 62.5 / 2 = 31.25 g
After fourth half life;
Amount left = 31.25 g / 2 = 15.625 g
That is the radioactive iodine - 131 went though four half lives.
How many days = Number of half lives * Half life
How many days = 4 * 8 = 32 days
Step 1 - Remembering the law of mass conservation
As stated by the law of mass conservation, in a chemical process no atoms can be created or destroyed. Consequently, the mass of the system will not change: the sum of the masses of reactants will be exactly equal the sum of the masses of products.
Step 2 - Using the law of mass conservation to understand the problem
The law of mass conservation therefore guarantees that, if we are mixing 7.2 g of C with 19.2 g of O, we will form 7.2+19.2 g of whatever is the product. Therefore we will form 26.4 g of product, which will be either CO or CO2.
Step 3 - Using mass percentage to find the correct product
Since we already know what will the mass of the product be, we can calculate the percentage of C in the product:
Now, let's calculate the percentage of C in both CO (28 g/mol) and CO2 (44 g/mol), remembering that the molar mass of C is 12 g/mol:
We can see that in CO2 the amount percent of C is exactly the same as we have calculated for the unknown product of this reaction. Therefore, the product is CO2.
Answer:
Both molarity and molality involves number of moles of solute
Explanation:
Molarity is obtained by dividing the number of moles of solute by the volume of solution in liters. Note that a solution is formed when a solute is dissolved in a given volume of solvent.
Molality, of a solution is obtained by dividing the number of moles of a solute by the number of kilogrammes of solvent.
In both cases, the number of moles of solute is involved. Hence, the number of moles of solute present is common to both molarity and molality calculation.
Answer:
Metal A will heat up faster
Explanation:
Step 1: Data given
Mass of the 2 metals = 1.00 grams
The specific heat of metal A is 0.568j/g* °c
The specific heat of metal B is 1.34j/g*°c
Initial temperature = 80 °C
Step 2: Calculate energy needed
A high specific heat value means that it takes MORE energy to raise (or lower) its temperature.
A low value means that it does not take very much energy to heat or cool it.
Step 3: Calculate energy needed to raise 1 °C
Q = m*c*ΔT
Metal A: Q = 1.00g * 0.568 J/g°C * 1°C
Q = 0.568 J
Metal B Q = 1.00g * 1.34 J/g°C * 1°C
Q = 1.34 J
We need 0.568 Joules energy to raise the temperature with 1°C for metal A.
We need 1.34 Joules energy to raise the temperature with 1°C for metal B.
Since we need less energy to raise the temperature for metal A, it will heat up faster.