Corinna Smith, 59, mixed three bags of sugar into the water before throwing it at 80-year-old Michael Baines while he slept.
She left him with 36 per cent burns to his body and told a neighbour “I think I’ve killed him”.
The day before the attack took place, Smith was described as angry and very upset at a rumour circulating about her husband that she believed to be true.
The court was told that Smith, also known as Corinna Baines, was also her husband’s carer.
Mr Baines was rushed to Whiston Hospital in the early hours of July 14, 2020 in a serious condition.
He died a month later on August 18 despite the best efforts of medical staff.
On the day of the incident, Smith returned home and filled a bucket from her garden with boiling water and mixed it with nearly 7lbs of sugar.
As Mr Baines lay asleep in bed, she poured the contents over his arms and torso and then left the property in the Wirral, Cheshire.
She then went to a nearby house and banged on the front door until the occupant answered.
He contacted police and ambulance after hearing her say “I’ve hurt him really bad, I think I’ve killed him”.
Emergency services found Michael in excruciating pain and whimpering in bed with the skin on his right arm and hand peeling off.
He was taken to hospital and remained in the burns unit for two weeks in a stable condition, before he deteriorated and died.
Smith was initially charged with grievous bodily harm but was later charged with murder after Mr Baines’ death.
On Tuesday a jury found Smith guilty of murder following a five-day trial. She will be sentenced on Friday, July 9.
Detective Chief Inspector Paul Hughes, from Cheshire Constabulary, said: “Smith killed her husband Michael in such a painful and cruel way.
“To throw boiling water over someone when they are asleep is absolutely horrific.
“To also mix three bags of sugar with the water showed the determination she had to cause serious harm.
“The sugar placed into the water makes it vicious. It becomes thicker and stickier and sinks into the skin better.
“It left Michael in agony and rather than call the emergency services, she wasted time by going to a house nine doors away to tell a neighbour, who she wasn’t close to, what she had done.
“Michael was an elderly man who fought for his life after the attack but sadly in the end he passed away. My thoughts continue to be with his family at this incredibly difficult time.”
Jayne Morris of the Crown Prosecution Service said: “Corinna Baines killed Michael Baines in a particularly brutal and painful way.
“She confessed to the manslaughter of her husband but the CPS refused to accept that.
“The CPS case was that her actions were deliberate and considered.
“She was clearly upset about the dispute between herself, her daughter and her husband, but the evidence demonstrated that she was in control and acted in anger when she poured the lethal mixture over her husband and wanted to extract vengeance.
“The Crown Prosecution Service said she intended either to kill Michael or to cause him really serious harm and so pursued a prosecution for murder.
“The jury have agreed with us and found her guilty. This is a tragic case that has devastated the family of Mr and Mrs Baines and our thoughts remain with them.”