Answer:
25
Explanation:
In DNA, Guanine pairs with Cytosine, and Thymine pairs with Adenine. This tells us that there are equal numbers for each Guanine and Cytosine, and Thymine and Adenine. When there's 35 Guanine, there should be 35 Cytosine that goes with it. 120 - 2(35) = 50. The remaining 50 nucleotides are Thymine and Adenine, and since they are the same number, divide 50 by 2. 50 ÷ 2 = 25. There are 25 thymine in the sample of DNA.
First we must understand the balanced chemical equation:
Pb(NO3)2 + K2CrO4 ==> PbCr04 + 2KNO3
This shows us that two moles of potassium nitrate are formed from 1 mole of lead nitrate or potassium chromate solution. The next step is to find out how many moles of each reactant there are. Note the word Molar is a concentration that simply means moles per liter.
2.25L of 1.5M lead nitrate = 2.25x1.5 = 3.375 moles of lead nitrate
1.15L of 2.75M potassium chromate = 1.15x2.75 = 3.1625 moles
The important part here is to see that the number of moles of the reactants are different. We know the number of moles of products will be dependent on the number of moles of reactants, and in this case there is less potassium chromate than there is lead nitrate, so this is the limiting factor as there is a one to one relationship with both reactants. Therefore, the number of moles of potassium nitrate produced is 2 x number of moles of potassium chromate. i.e. 6.325 moles of potassium nitrate is liberated.
To work out the number of grams, we must find the molar mass (the mass of one mole) of KNO3, which is the sum of the molar mass of each of its component atoms that make up the molecule. I've looked this up as 101.1 grams per mole.
Now we simply times the molar mass by the number of moles to yield the final grams liberated: 6.325 moles x 101.1 grams/mole = 639.4 grams of potassium nitrate is liberated from this reaction.
Answer:
Scientists often use models of Earth to study the movement of earth and it's moon. They figure out what the distance is from the moon to the point between earth and moon where the gravitational pulls of earth and moon are equal.
