3. The two most abundant isotopes of copper contain 34 and 36 neutrons. If the isotope with 34 neutrons comprises 72.5% of all copper, what is the average atomic mass of copper?

63.55 amu

Explanation:

The average atomic mass of an element can be calculated by multiplying the decimal abundance of each isotope of that element by the relative atomic mass and summing them up. That is;

Average atomic mass = {atomic mass of isotope 1 × decimal abundance of Isotope 1} + {atomic mass of isotope 2 × decimal abundance of isotope 2}

According to this question, two most abundant isotopes of copper contain 34 and 36 neutrons. The atomic mass of each isotope can be found by adding the no. of neutrons to the atomic number/proton no., which is 29.

Atomic mass of Isotope 1= 34 + 29 = 63

Atomic mass of Isotope 2= 36 + 29 =65

Decimal abundance of each isotope = percentage abundance ÷ 100

Isotope 1 (with 34 neutrons) = 72.5% = 72.5/100 = 0.725

Isotope 2 (with 36 neutrons) = 100 - 72.5 = 27.5% = 27.5/100 = 0.275

Therefore, the average atomic mass

= {63 × 0.725} + {65 × 0.275}

= {45.675} + {17.875}

= 63.55

Hence, the average atomic mass of copper is 63.55 amu

helicase, i think thats it

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.