Adhesive Transfer

please help me with these net charge prolems??? i have tried them all and failed miserably?

Find the net charge of a system consisting of each of the following.
(b) 157 electrons and 235 protons
??? C

A container holds a gas consisting of 1.96 moles of oxygen molecules. One in a million of these molecules has lost a single electron. What is the net charge of the gas?
???? C

When adhesive tape is pulled from a dispenser, the detached tape acquires a positive charge and the remaining tape in the dispenser acquires a negative charge. If the tape pulled from the dispenser has 0.26 µC of charge per centimeter, what length of tape must be pulled to transfer 4.0 1013 electrons to the remaining tape?
??? cm

A system of 1486 particles, each of which is either an electron or a proton, has a net charge of -6.304 10-17 C.
(a) How many electrons are in this system?
??? electrons
(b) What is the mass of this system?
??? kg

Okay I worked these out. Hopefully they are right.

Find the net charge of a system consisting of each of the following.
(b) 157 electrons and 235 protons

(protons-electrons)(1.6E-19)
(235-157)(1.6E-19)
Answer= 1.248E-17 C

A container holds a gas consisting of 1.96 moles of oxygen molecules. One in a million of these molecules has lost a single electron. What is the net charge of the gas?

(# of moles)(6.022E23)(1/(10^6))(1.6E-19)
Answer= .18885 C

When adhesive tape is pulled from a dispenser, the detached tape acquires a positive charge and the remaining tape in the dispenser acquires a negative charge. If the tape pulled from the dispenser has 0.26 µC of charge per centimeter, what length of tape must be pulled to transfer 4.0 1013 electrons to the remaining tape?

(electrons*1.6E-19)/(charge in C)
(4.0E13*1.6E-19)/(.26E-6)
Answer= 24.615cm

A system of 1486 particles, each of which is either an electron or a proton, has a net charge of -6.304 10-17 C.
(a) How many electrons are in this system?

(1/2)[1486-(-6.304E-17/1.6E-19)]
Answer= 940 electrons

(b) What is the mass of this system?

(1486-940)*(1.67E-27)+(940 * 9.11E-31)
Answer= 9.127E-25 kg

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