Cho m gam hỗn hợp Fe và Zn có tỷ lệ mol 1:1 vào 100ml dung dịch CuSO4 0,9M thu được m gam chất rắn Y. Tính giá trị m?

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Cho m gam hỗn hợp Fe và Zn có tỷ lệ mol 1:1 vào 100ml dung dịch CuSO4 0,9M thu được m gam chất rắn Y. Tính giá trị m?
Giải:
Số mol Cu n=0,9.0,1=0,09
Do tỉ lệ mol là 1:1 nên n=nFe=nZn=m/(56+65)=m/121
=>m=121n
Vì Zn mạnh hơn Fe nên Zz phản ứng trước.
Zn+ CuSO4 -->ZnSO4 +Cu
n…………………………n
khối lượng Cu tạo ra là 64n
do MCu=64 < MZn=65 nên ta có:
mgiảm =mra-mvào=mZn-mCu=65n-64n=n.
do Fe và Zn cùng số mol nên nếu Fe cũng phản ứng hết thì khối lượng tạo ra không thể bắng m, do đó Fe dư một phần.
Fe+ CuSO4 -->FeSO4 +Cu
n’…………………………n’
khối lượng Cu tạo ra là 64n’
do MCu=64>MFe=56 nên ta có:
mtăng=mvào-mra=64n’-56n’=8n’
do khối lượng kim loại trước phản ứng bằng khối lượng kim loại sau phản ứng nên:
Δm=0<=>mtăng-mgiảm=0
=>8n’-n=0
Ta có hệ:
ü n’+n=0,09 (số mol Cu)
ü 8n’-n=0
=>n’=0,01 mol, n=0,08 mol.
Vậy khối lượng cần tìm là: m=0,08.121=9,68 g.

Nếu bạn nào chưa học phần tăng giàm khối lượng thì xem ở đây: Giải bài toán bằng phương pháp tăng giảm khối lượng.

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